Have you considered an MMA ground and pound dummy or a wrestling throw dummy?
There are several types out there and not all of the work.
I would consider looking for one with full length arms and is sturdy enough to nearly stand on it's own.
Some examples: Throw Dummy: Ground and Pound:
Personally I think the throw dummy would work better than the ground and pound dummy.
martialarts.stackexchange.com/users/66/Beaker
A gi and a pole is all you need!
I had support beams readily available when I was training in judo.
Put your gi on the beam, and you're good to go for a lot of different throws.
It works pretty well for uchi komis for throws like o soto gari , o goshi , seio nage , and the like.
Not the best for o
uchi or ko uchi gari though.
To make it a little more interesting, or add resistance, put a resistance band through the sleeves and grip that instead of the gi sleeve.
martialarts.stackexchange.com/users/21/Patricia
As Iaroslav said, some sort of elastic resistance equipment around a sturdy pole is your best bet.
Personally I have found that resistance tubes ( http://www.amazon.co.uk/Reebok-Resistance-Tube-Level-Black/dp/B002KMK57O/ref=sr_1_4?s=sports&ie=UTF8&qid=1328173425&sr=1-4 ) are better resistance wise, however the bands ( http://www.amazon.co.uk/Dyna-Band-Purple-workout-resistance/dp/B00293SIVO/ref=sr_1_8?s=sports&ie=UTF8&qid=1328173425&sr=1-8 ) can provide a more realistic gripping position.
For an even more realistic method you can take apart an old gi and attach parts of the lapels to the handles of a resistance tube and grip that instead of the band itself.
martialarts.stackexchange.com/users/117/Jamie MacDonald
I've seen some people using elastic rope attached to a wall to to practice certain throws.
Elastic bandage is widely used for that.
Thus it is not good for every throw, but is rather cheap and simple to use.
martialarts.stackexchange.com/users/91/Iarek
You can't.
Not effectively that is.
Other answers are telling you to simulate static throws.
I avoid teaching static throws, generally.
Moving drills are the most effective in my experience.
Timing is crucial.
Reap the foot just as he is placing his weight on it.
Ko Uchi Gari , Kodokan Judo, page 69
You can't do a proper Ko Uchi Gari without having the proper timing.
You cannot develop this timing when training by yourself.
All of your technique should have a timing element.
[Edit]
We once had a guy come in and tell one of our teachers that he was a black belt.
This dude had never taken a Judo class before.
I don't know what books he had read or drills that he had done (if any).
Self-taught self-trained Judo black belts don't exist.
martialarts.stackexchange.com/users/10658/tye649
A traditional response to this, particularly in Shinden Fudo-ryu, was to use trees or bamboo.
In positioning yourself for the throw against the tree, you are performing a form of isometric exercise to adapt your body and tendons to the motion.
In performing against bamboo which flexes and moves, you become capable of following the movement through.
martialarts.stackexchange.com/users/25/stslavik
I find that you can practice foot work and here your arms would be on your own
but I would recommend doing it in front of a full length mirror so that you know if it looks the same as when your sensei does it (if you have one) if you know what muscles you need to work on for a move or throw then you can try and train them in other methods for example pull ups or push ups or squats.
I find this is useful from personal experience.
martialarts.stackexchange.com/users/10586/ren
You can practise Judo at home if you have a good grappling dummy that consists of a whole body such as torso, head, arms, and legs.
The only issue you will have is the resistance because in real life when you go to execute a Judo throw on someone you will be met with some resistance.
Still, learning the Judo throws at home and using a grappling dummy will help you when or if you join a Judo school.
Also, if you want to add more to the Judo techniques such as knives, guns, etc then practising them at home on a grappling dummy would be more beneficial as in MMA, Jujitsu, and Judo schools will not add the weapons to the techniques.
martialarts.stackexchange.com/users/10665/The Real Joe 8.2
How do you practice your judo throws at home or any time that you're by yourself?  The leg movement is easy to do as long as you have the space, but proper arm movement and strength is hard to simulate.  I've tried tying a belt to a post around shoulder height and some sort of cushion at hip level. It's decent, but not that great.  Any suggestions?
How do I practice judo throws on my own without a partner?
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<judo><training><drills><throwing>
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martialarts.stackexchange.com/users/71/Moox
Although some people avoid teaching static throws, others say that a gi and a pole is all you need. Trees, bamboo, elastic bandages or ropes can all be used as solo training tools. You may also use a grappling dummy. However, timing is a key factor for all techniques. You can practice Judo at home using elastic, practicig timing, moving drills or  using a whole body dummy.  
Suggestions to practice Judo at home include the use of elastic, practicig timing, moving drills and you could use a whole body dummy. 