This is a confusing one. If a fish is bloated because it has an intestinal blockage then initially I wouldn't medicate at all--I'd stop feeding and add Epsom salt to help things move along. If a fish is bloated because it has bloat, well, fish that have bloat don't eat. :?
mudkicker's fish sound like they have bloat until you get to the brine shrimp eating part. Perhaps brine shrimp is just impossible to pass up--even for a fish that has bloat?? I honestly don't know.
But getting back to your question: how to dose metronidazole with brine shrimp. Not sure if brine shrimp is the best way to go as far as a met-vehicle, but I think I would first of all finish out the JPC, (which contains metronidazole) and then if the fish are eating and swimming normally there's really no need to feed them medicated food. Bloat is thought to be caused when the fish comes under some sort of stress, (rough handling, aggressive tank mates, poor water conditions, etc) and the flagellates that normally reside harmlessly in the fish's intestines suddenly increase in numbers and overwhelm the fish.
So if your intention is to ward off future bloat episodes the best plan is to keep the tank as stress-free as possible.
Whatever treatment you choose: fit in as many partial water changes before, during and after treatment as you can. It's believed that bloat is spread when healthy fish mouth infected feces so the water changes and gravel siphonings will help with that but I've also read that the flagellates may have a free swimming stage during an bloat outbreak so the water changes and gravel siphonings will help in that regard also.
If you choose to feed fish metronidazole soaked food--food of any kind, then I would go with the dosage that GTZ recommended.
Robin