Hi Joe,
I wrote a translator awhile ago to turn Gazebo sensing element
messages into the PressureState messages the PR2 finger sensors use.
I've stuck it in
https://code.ros.org/svn/wg-ros-pkg/trunk/sandbox/sim_contact_translator
.  It runs fine, but I haven't used it in months, and I haven't had
time to test whether it still works yet.  You're welcome to try it
out.

-Kaijen