I'm on the way to hit the sack, but here are some quick comments/thoughts...

To start with, I'd recommend looking through Dimension3D's various tools.  I seem to recall being able to pose figures in one of his tools (which may have also been a morph-generation tool), but I don't recall the particulars. Another place to check would be PhilC's stuff.

Barring any existing tools, my only 'quick' comment is... divining Poser's rigging system shouldn't be under-estimated.  Each joint has it's own axis and rotation order and once you get that far, you still have to contend wiith the blend zones, spherical fall-off zones and (potentially) bulge settings (noting that all of those can and often are set differently for each axis). You may not be talking/thinking about messing with all of that though, depending on your approach.

If you want to just use Poser Magnets on the figure, posed inside Poser, the trick is in getting the magnets (zones) place correctly... which is obscured by the pose itself, so you kinda have to figure out which vertices you want to affect, then un-pose the joint and get the magnet and zone set up, then re-pose it and twiddle with the magnet - not a lot of fun :).

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