So I've got a friend who's unabashedly Sim. I've been talking to him about Capes and he'd like to give it a try, but he and I are both pretty aware that his preferences lie in another direction. How would you go about bridging the gap?
I wouldn't.
Instead, appeal to his sense of adventure. Get him to open his mind.
Trying to sell it on sim grounds is like trying to sell an H3 because it's smaller than an H2.
I think that diceless games can be the most simulationist games out there. (stay with me, I know Capes isn't diceless). I played in an Amber campaign in which everything that happened happened from a Sim perspective. And especially if you're the GM, a diceless game can simulate exactly what you think would happen in every situation. There's no situation where you have to say to yourself "well, that never would have happened, but the dice came up that way."
In Capes, task resolution is diceless. If you want to play Capes from a Sim perspective, then task resolution will simulate what you're trying to simulate perfectly on your turns. Conflict resolution won't, but task resolution will.