as abel, couldn't you just roll through it? Granted, that doesn't punish the ball but you could just keep rolling until the blanka gets bored and does something else and you won't be taking any damage yourself.
Other good options, depending on your skill in timing them, would be a jump backwards and kick to kick him out of the air, or I think a well timed overhead kick would beat the ball. Whatever that move is where he jumps and spins with his heel.
Even if it trades, blanka takes a tooon of damage if hit out of his ball so trades will be in your favor. If your timing is really good you can also just punch him before he hits you I believe.
I'm also not sure, but would guess, that you can ultra a blocked blanka ball and it will hit.