Jim:
I would find it very unusual to do a hoisting (rescue) exercise with much beyond an airframe, fuel and a small crew. If an S-92 has Category A perf with a full load of pax and fuel, it would stand to reason (and I'm more than willing to be corrected) that it would have a HOGE OEI capability for enough duration to complete the hoist.
Sounds like someone at Sikorsky needs to do the performance charts that way.
This sort of thing has happened before - perf charts need to catch up with the operations.