i prefer to use an exacto knife to remove the feet from the platform. lay the figure on it's side, place the blade at the base of the foot and rock the knife back and forth while applying pressure, and you will create a clean edge for reglueing.
lighter....don't hold the flame to the figure for too long (not more than a second or two at a time), and keep the flame moving across the part. don't just stick the flame in one spot and leave it there, unless of course you are trying to create the human torch.
be ready to work quick, because the plastic will get very soft, very quickly. another option is a heat gun (paint stripping gun) from a hardware store. this MIGHT make things easier, but you may run the risk of melting the entire figure all at once.
whichever you go with, i think that the most important thing is to not apply direct heat/flame to one spot for more than a couple of seconds. now that you've melted a couple, maybe practice on their other limbs to get the hang of just how long to apply heat.
hope this helps.