Steal away! Green Stuff is plumbers epoxy filler generally favoured by Warhammer/GW miniature modders and sculptors. It comes as a strip of half yellow and half blue and you mix the two to make it turn green. Once it's green you can shape and mold it. It's really really sticky and sets within an hour or so, so you have to work fairly quickly with it. Unlike the other fillers around this stuff sets and becomes more like a form of PVC, so it's more appropriate for working with plastics I figured.