once you have merged the two models together, you will have to export the new skin template from the skins menu. it should have the skin of the two models on it. you may also have to move some faces and resize some parts of the models skin template so it will all fit. then, you have to repaint the single skin with both the models.

does that make sense?!

so, to answer your question. no, i don't think so or at least i haven't heard of a way.