I did not actually find it needful to export item by item. I've found that if I build in the Assembly room, group, and export the group as a Wavefront obj what is created is a single obj file with the proper "g" groupings used by Poser. If I build entirely within the vertex modeller (my current method) I merely have to use the command "name polygon" to create the needed groups. I've found that Carrara doesn't always export materials mapping zones, however, and rather than fight with it I've taken to naming groups of polygons for materials mapping purposes, exporting the obj, using UVmapper to unfold the map properly, then running the obj file through BBedit (or another text editor) to convert most of the "g" statements into "usemtl" statements.