Hold up folks...

In this case, you can have your cake and eat it too. :).

There's no reason to 'scale it all to fit within a single 0.0<->1.0 UV space'.  A better approach is to 'tile' it into multiple UV spaces.  So in other words, the 'face' map would take up from 0<->1, then the 'torso' might be found one unit to the right, in the 1.0<->2.0 space and then the 'limbs' might be another unit to the right, in the 2.0<->3.0 space, etc.  (you can tile them out in any of 4 directions, including negative values).

Most (all?) apps will treat all of these "outside the range of 0.0<->1.0 UV space"  islands as if they existed in the 0.0<->1.0 UV space.

This solves the issue with Zbrush and the file still works fine inside Poser, C4D and likely most any other 3D app.

(shameless plug:  for C4D users, I have a plugin "Undertow" which has 'TileU' and 'TileV' commands in it to assist in thi type of thing)

Cinema4D Plugins (Home of Riptide, Riptide Pro, Undertow, Morph Mill, KyamaSlide and I/Ogre plugins) Poser products Freelance Modelling, Poser Rigging, UV-mapping work for hire.