My group runs Hexing two different ways depending on the scenario.
Sometimes, the GM just offers a compel, which you can buy off as usual. Harry might have bought off the first compel, but accepted a second one later or something like that.
Other times, the GM asks the player to roll discipline against a difficulty determined by the power of the character and the level of tech involved. In this case, a potion, spell, maneuver, etc. could be used to boost or substitute for the roll just like for any other skill check.
So, for that model, Harry might have placed a discipline maneuver before going to the show, "Trying to Stay Calm", and set up a spell that applied an aspect "Power Under Control". He tagged those when it looked like he might fail a discipline roll, but eventually ran out of tags as the scene got more and more stressful.