I don't have a recipe for you but I can move this thread to the main discussion forum (with a copy in the original forum as well) to help you get more feedback...
FWIW, I think you'd just be better off doing a waterchange to adjust your bromide and fluoride levels. Remember anything you add you should test for on a regular basis so that you don't end up w/ an imbalance. For the cost of the two test kits plus the cost of the materials to make your own additives, you could do a lot of waterchanges.
I just checked PremiumAquatics.com and couldn't find test kits for these ions so IMO you'd be better off just doing the monthly waterchange song-n-dance if you asked me.
While that may be true, if it were a real problem, I'd surmize that we'd all have problems keeping corals. Since this doesn't seem to be the case, I'd say that it's something that I wouldn't worry too much about.