That is the basic workflow I use as well. I generally solve the whole "no displacements across UV boundaries" problem with a combination of the suggestion above (split into multiple OBJ files), avoiding too much displacement around the boundaries as I morph, and then manually "blurring" the edges (in a paint app) of the textures for the areas that border other maps (such as the neck borders in the body & head maps). It means you have to remember a few more things while using ZBrush & there is a little extra work afterwards; but it can give you some very good results. There have been alot of people complaining about the whole "one mesh, one map" problem to Pixologic, so perhaps they'll be fixing that in their next release (which already has some cool new features).