I haven't seen anything for soft body dynamics (Poser Physics is for rigid body dynamics).

The closest thing is probably ockham's Jiggles script, which requires morphs.
It's described in http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=1682114
and http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=1671230
(this is the post-upgrade style link for the one that appears in the first thread).

Make sure you download from VP, as that's the most upto date version.