Tank isn't much of a toy rabbit. So far, the only toys he likes are things he can eat (cardboard and paper.) All he wants to do is shred them and dig holes in them and eat them. 

I've tried the baby keys and perscription bottles for him to toss around, but he's indifferent to it. If I switch his boxes for cardboard with different textures or switch a phonebook for a news paper here and there, (and of course toilet paper rolls!) he'll be entertained for a while.

But after about six weeks he gets bored with them and wants to chew on the bars of his cage. In a week or two he'll get back into them, but in the meantime he's eating his cage. I don't like that. I  don't want him to be bored! I let him out to exercize for about four hours every day (which I think he spends maybe ten to twenty minutes of actually exercizing and the rest loafing around in his cage anyway, lol) but he won't play with anything else !

Has anyone ever heard of a rabbit eventually learning to play with stuff? Maybe if I leave certain toys in there, he'll get it eventually?

Your bun is playing. I actually have a bun, which, when described to the vet, was told that most likely, he never learned to play his entire life. She told me he probably grew up in shelters and will never learn since he's an adult now even though his wifey loves to play.

Yes, chewing the cage bars indicates that he does enjoy chewing. My suggestion in that case would be to get him some willow toys. A favorite of Sammy's turned out to be the huge unpeeled willow bark ball, or the big willow cube, that you can order online. (Here or other rabbit supply stores.)

It was the only time I saw her stand up and toss. She loved grabbing the ball that was as big as she is, lift it, toss it down, then chew off a piece of it. It takes her a couple of weeks to completely dismantle it. Meanwhile, the pieces are chewed, pulled around the floor, and generally good for teeth and fun.