If I need to melt margarine on the stove and have no pots or pans available, can I melt it in a thin disposable aluminum pan directly on the burner (on a low flame), or will the pan burn/melt? 
Butter melts at such a low temp that this would work. You would want as low a flame as you can.  I would not recommend it, however. If you forget it the metal is thin enough to burn through and at least make a mess- worst case it will ignite the butter, atomize the aluminum which will unverifiably hasten the onset of Alzheimer's, and burn your house to the ground.  Butter melts at 90-95F. You can just leave the butter in the sun for a few minutes. 