All you need to do is export only the body parts you want to an OBJ file.
When exporting, click on the "UNIVERSE" box to clear everything, then select those body parts you want.
The options you want on the next dialog should be only "Weld body part seams" and "Include existing groups in polygon groups".
You can new load the OBJ you created and it will have the grouping and materials of the original body parts, but it will be a single object.

Strictly speaking, you don't really need the grouping for this, unless your planning to rerig as a figure so that you can use the morphs.