I don't think it is a good idea to put a semi-aggressive fish in there for that reason. It would possibly end with a dead ram. I wouldn't add corys until the rams sort themselves out. Some people do indeed have issues with rams nipping and harassing corys, and since you have a bossy ram, I would avoid corys for the moment. I wouldn't add an apisto. They are a bit feistier than rams, and I think that would cause problems.
I don't like hatchets either.
The best thing I can think of right now would be a small school of another peaceful tetra, like the rummy nose tetra. Middle dwellers will naturally move up the water column a bit when the bottom of the tank if full.
Another option would be a pencil fish. They are pretty as centerpiece fish.