I just use Poseray, copy materials to groups, delete checked/invisible groups (like teeth...), merge groups that use the same material (give it the name of that common material), after having left maybe 5-10 groups (so, each using one material), go to materials tab again, copy groups to materials (you'll loose materials it says, and they'll all turn white), copy the name of the material (and possibly path) into the box, apply... and it should be back. Or relink to that material. Then export.
What I also do is save the nodes needed for a certain object/model as tgc. In that case relinking isn't even needed, just open in TG and relink the imported tgc nodes to the necessary parts' nodes. If I make myself clear....
Oh and no, if you save as jpg or LZW tiff, it'll still be expanded in TG. Only thing is to reduce size from 4k to 1-2k or so, if possible for distant views.
I don't think it can be one part, as the UV's of those parts usually overlap. But in some cases that may work.