The player will have to choose between getting his girlfriend out of the building and letting it blow or trying to disarm the bomb and risking both of their lives.
I agree with you, but I'd modify it slightly. I have a hard time seeing all that number of exchange stuff being a fun compel because playing out the conflict to determine the number of exchanges and then compelling the aspect to reduce that number is minutia that can be handled better in other ways.
But, the quoted part is great. So, I say forget the skill challenge. Get to the meat of it and hit the player with a Compel on their Better Late than Never to say that when they get there they have the dramatic choice of being 100% sure that they save the girl at the expense of the building or deal with the bomb, but with a juicy risk.
Assuming the choice is meaningful to the player, and the GM knows how to make either choice lead to more great scenes, then you have a "compelling" moment (see what I did there?).
