Hello people, I'm rayera, compose is needed if you want to use smooth and inflate tool without problems (try this tools in the seam of two groups), it's not a Blender problem, this procedure is needed for doing full body morphs in Zbrush as well, but if you don't use this tools you can do it in this way:

1. Export you figure from pose using only Include bodypart name in poligon groups and As morph target (no world transformation)
2. Import your character to blender using ONLY Morph target option, and clamp scale set to 0
3. Do your morph but remember not to use Smooth or inflate.
4. Export your morph using only Rotate X90 and Morph target but don't overwrite the original obj
5. Load the morphed figure in UVMapper (yes I know you wanted to do it all inside Blender, but it's the easyer and faster  way IMHO (and UVMapper is an aplication everybody use and have ), you'll be alerted you figure have no UVMap, don't care about it, go to File/Import UVs or just press CTRL+I and load your original obj exported from Poser, save you morph with the default options
6. Import your morphed figure in Poser, with all options uncheked, now you can spawn the body parts in props with the groupping tool, load your charater and inject the morph with the wonderfull script I provide whith my tutorial, or export part by part as obj using only As morph target (no world transformation)

Hope I've been useful.