fit nicely over the break and slide it on so you can still put glue onto the break.
dab some glue on the ends of the broken part and also on the dock. leave a few minutes until its tacky then put it together. make sure it will set in the right place.
slide the heat shrink over the break and shrink it. this will help hold it all together.
i used a rubber band cut from a bike inner-tube because it was what i had to hand.
leave it to cure and you're done!
oh and one more tip: to release your phone from the dock push it out from behind rather than push 