Are you making a prop or is it an existing prop? I've never heard of swapping UVs inside of Poser, but then I didn't know DAZ Studio could do it internally, so that's not saying much :-)

How are the extra UVs stored, as another obj file or in some other format? The obj file format itself can only contain one set of UVs, so I take it you have 2 objs, each with different UVs? I would think the easiest solution in Poser would be to make 2 props, one pointing to each of the obj files. Or if you have one prop already, just edit the pp2 file changing the line that calls the geometry file, make it point to the other one.

Edit: I've just had another thought: Geometry swapping is possible in Poser (or it's possible to make figures and maybe props which exchange one chunk of geometry for another at the turn of a dial) so they would swap UVs too. I'll leave it to someone more knowlegable to tell you how to do that though, I've done it before but I can't remember the process.