If you don't have a strap wrench, an old serp belt and some vice grips can be used to improvise one. It won't be as effective, but you might be able to get the bolt tight enough. Put the belt all the way around, clamp down on the belt with the vice grips with the tightening bolt side facing counterclockwise. As you tighten, the vice grips will roll back on the belt and help grip better, and will help you hold the pulley while you tighten the bolt.
If you want to use the pry bar method, screw a couple of bolts into the holes that the puller screws into and use the pry bar against these screws (assuming the LS uses the same three point puller method that every other car I've ever worked on uses). It's better than wedging the pry bar directly against the damper, especially since wedging against the damper almost always means sticking it between the pulley and the block which would affect your torque reading. I wouldn't use the puller bolts for this though, because this can bend the bolts being used and you will want them for next time the puller is used. You will also want to thread the bolts all the way through the damper, or as far as you can get them into it to keep from damaging those threads.
