<<I am still furious with his previous owners for treating him so badly>>
I think you are wasting your energy and time. Do you think that this sort of people are thinking of the rabbit right now? I dont think so. And I dont think they were thinking doing good. Probably they only wanted to get rid of the rabbit...
OOps now you are going to feel angrier!! But really it is better do not think of them.
One day I rescued a rabbit that was alone on the pavement. Since there were cars coming I jumped to him, hurt my knees (there were little stones there) and I asked to somebody if she knew where the owner was. The lady took me to a neighbour's house. There was nobody and we saw the empty cage in the garden. We only put the rabbit into the cage with a big rock on the top to avoid escaping. Some days later, I visited the person to tell him the rabbit had escaped. He only said ah yes yes thanks, but I saw he really did not care about the animal...
what else could I do?