Your problem may be the way bunnies feed. Like kittens, they sort of curl their tongues around the nipple, and of course a sponge wouldn't give them the structure to wrap around. But every day he lives is a little victory for you at this point.
I'm not sure how much stimulation a bunny needs to get them to pee. I've heard that they do it on their own, with the movement of the others in the nest being enough to make them all go at once. Certainly, anyone who has had litters knows that handling the kits before they get their eyes open will get you pee'd on, sooner or later (I had a rabbit-raising friend who told me this was one of her ways of figuring out if a kit was a boy or a girl - with a girl, the pee just sort of dribbles down the tail, if it squirts you right in the eye, it's a boy!)

I'm not sure how much stimulation a bunny needs to get them to pee. I've heard that they do it on their own, with the movement of the others in the nest being enough to make them all go at once. Certainly, anyone who has had litters knows that handling the kits before they get their eyes open will get you pee'd on, sooner or later (I had a rabbit-raising friend who told me this was one of her ways of figuring out if a kit was a boy or a girl - with a girl, the pee just sort of dribbles down the tail, if it squirts you right in the eye, it's a boy!)