Jemax,
You can work out a rule of thumb yourself man.
On a nil wind day, note your power for an IGE hover. Take off and then fly S&L at 500' above that elevation at BROC. Note the difference in the power required.
Then you can say to yourself, S&L at 500' above my anticipated landing DA at BROC, IGE hover power is X amount above what I'm using now.
Experiment a few times, and at different DA's.
But it will certainly get you in the ballpark, and you can apply it to any model of helicopter.
And don't forget the performance charts either.
Comprende?