I personally use UbS for Horridon, but I haven't gotten to heroic yet. Having said that, you might be better off keeping UbS for yourself, and having the others swap over to Clemency. Just so that you can have DP up more often. If you choose to go with Clemency, you can HoP yourself more often instead of just bubble.
I don't recall if you can just HoP someone before Triple Puncture goes off, have them taunt the boss so he stays on the tank, and then click HoP off after Puncture. Would require some considerable timing to pull off, but would be a way to mitigate one of the TP's and remove any stacks on said tank.