I say let Bard start in the 4th spot and either Cook/Padilla/Doubront in the 5th spot, or maybe even split time at the 5th starter's spot to see who does better. Then in June/July/Whenever Dice comes back, move Bard to the pen, and move Aceves into the rotation, and make Dice our long reliever/swingman. I don't think he'll be ready to start necessarily when he comes back, so why not let him get some pen work instead. He may be useful from that position.
That way they can limit Bard's inning count by splitting him at setup with Melancon, or split at him closer with Bailey. Aceves probably wouldn't have thrown as many innings as Bard by this point, so having him do a little starter's work shouldn't be a problem.