Thanks for the input. I've decided that what I'm trying to do probably isn't possible though.
It's turned out to be no trouble at all to assign different shaders to different areas of one mesh. If it is all one mesh though, it's all one set of UVs, and even if I do use seperate image files on different parts, the parts still occupy the same (smaller than they would otherwise be) space in the UV layout, making it pointless.
I'll live though...just would have been nice
I consist of mostly water.