you have come across one of the achiles heels of poser figure creation. frankly the only shortcut that works is not to use poser for grouping at all, which is what almost all merchants have done. if you have a modeler that can do .obj grouping I would use that, or UVMapper can do it, or Autogroup editor availible here. as for selecting backside polygons at the same time as you select frontside in the grouping tool you can change over to wireframe view and both front and back polys will be selected.