The best way to do this (having done this several times, I know from experience): Once you get your model the way you want it in Rhino, mesh it, then save the Rhino 3DM file. This is the most important step. Export the normal version as OBJ, import this into Poser. Go back to Rhino, do not re-import the OBJ into Rhino, re-open the 3DM you saved earlier (unless you still have it open), and modify it, then export the results as OBJ again. Use this new OBJ as the morph target in Poser. Rinse and repeat as needed.