There are a lot of things not implemented in the game that are actually in the HPL2 tools. "Bullet damage" is there if you look for it
Anyways, it might not be a feature that is supported, so you may be out of luck. But try this:
Check GrabUseOffset and write the X, Z and Y values with commas in the first and second fields.
GrabPositionOffset: 0.2, -0.1, 0.3
GrabRotationOffset: 0, 15, 0
I've got another idea I can try later on, but see if that works for ya.
It worked? Wow that was just a wild guess! I have an inkling as to what exactly you're intending to do with this offset business, but I want to be surprised