I've got about 11 ghosties in with my pig of a CT. He has very similar behavior, but I've got a routine that keeps his overfeeding down, and the shrimp still get fed.
1) Using a turkey baster, get a full squirt of tank water in a small container (like the betta cups, or smaller if possible)
2) put a small pinch of flakes in the cup
3) Squirt in more tank water, causing most of the flakes to sink
4) Suck up a decent number of flakes with the baster
5) Find where the shrimp are hiding, and using the baster, give the food directly to them (it helps keeping the betta distracted with his own food, especially if the shrimp are on the bottom)
6) If the betta does go for the food before the shrimp can eat, chase him around a bit with the baster. I've had to do this several times, just be careful not to hurt him.
With this, my betta will still get a few flakes, but not enough to bloat himself off of it. Keep in mind that ghosties aren't really algae eaters. They'll eat it if there's absolutely nothing else in the tank for them, though. They very much prefer their own food or dead/dying plant matter from aquarium plants.