Given the number of White Court vampires, yeah, hunting down a magical solution would be insanely risky. And remember the guy who said he'd die to be able to 'play like that'? Unseelie pacts would be just as dangerous.
Still, given the risks involved in RW wonder solutions to excess weight, it might still be worthwhile!
As a sideline of a PC I created with a Demesne, I decided to justify his Resources by him providing feasthalls of suckling pig etc to the local Jenny Craig; since the food turns to ectoplasm/evaporates when the clients leave the Demesne, they can gorge without weight gain. All the side effects of gorge/vomiting of course, but he wasn't a terribly nice PC.
Btw, would that be the main reason not to accept food from the Fae? You risk starving to death if you've been living on it? Or does it also open you up to Fae magic?