To do the grappler reversal, you just need to set your character class in pedstats to grappler and make one of the Grapreversals stats to 100 (STAT_BOSS_RUSSELL has it on 100). Then, just allow one of the jocks to attempt a knee drop on you, and it will be reversed.
The Powerbomb, only way is through his boss style, which is randomized between it and the Boston Crab. The chest thrust is done by hold "X" (look behind button) and then pressing either attack or the run button, I forgot which one exactly.