Griffo,
I was surpsrised too, but on checking the RFM I see that there is indeed a back up procedure for elevated helidecks! I would have thought it was intended for hospital roof tops and the like - not Jack Up Rigs
By the way, I don't believe this procedure would have any adverse effect on the tailboom heating relative to the overall useage - there are too many variables and too brief an exposure. Heating from exhausts can be an issue in general though, and I know a previous type I flew had a modification to the tail rotor drive cover for this reason.