Gojj's suggestion was the first thing I thought of as well. I'm not sure if I like the idea of a milestone happening right before a fight, but that could work. Especially as that seems a cool story.
Edit: Huh, odd. gojj and Arcane posted at the same time, as did me and Jack. Interesting. Anyway, to expand on what I said above, gaining powers for a scene requires a fate point per Refresh gained, so it seems fair that it could work backwards - losing them for a scene, so long as they'd actually be relevant, should give fate points (maybe, in this case, representing the "burst" of free will gained after giving up a coin. Defeating the Denarian should probably be enough for a milestone in any case, so he could then reorder his Refresh.