To make full body morphs across groups in P7, just import the figure's original object file from the geometry folder.
It is grouped but still welded so that it doesn't break apart when you use the MorphBrush.

Once you're done morphing, export the modified mesh and reimport it back into Poser. This makes the morph permanent.
Then use the SetUp room to turn the morphed mesh into a moveable figure again.
Then do the joint fix morphs if necessary.
After your finished morphing, just save your figure or create injection morphs for redistribution.

BTW, Z-brush can't work across groups unless the Poser mesh is properly welded, either.
Try to export a Poser mesh from the Poser viewport as an object, then load it into ZBrush and try to smooth it.
It will break apart.
Load the same object directly from the geometry folder and it will stick together.

The only real problem there is if you want to morph a figure that was already morphed inside Poser with it's default morphs because then you'll have to weld the mesh during export and Posers welding renumbers the meshes vertices and that renumbering makes all default morphs useless.

There are ways to circumvent this with a Python script (Cage and Spanki are HEROES ! ), but it's pretty complicated.

(But once you really learn the Morphbrush you don't really need the default morphs anyway. For my custom characters I pretty much only keep the vertices of the head in their original suquence so I can still use the expression morphs. But again, ZBrush has exactly the same problem.
If the mesh isn't welded, it breaks.
And if you re-weld it during export or in a modeller, say bye bye to the original morphs later)

As I said, there is a way to swap morphs between of the same geometry meshes but with different vertex numbering, but it isn't easy.
It would be indeed a big help if both the MorphBrush and ZBrush could reweld meshes "on the fly" without renumbering vertices.