I export the body part out of Poser as an obj file, with these options checked:
Include body part names in polygon groups
Include existing groups in polygon groups
As Morph Target (no world transformations)
Load it up in Lightwave, shape it, export it as obj file.
Load the obj file in Poser as a morph target.
The MTL file won't mess up the vertices.
And my workflow is ancient, so there might be a better way nowadays.