How can I convince my sheep to regrow their wool?

We have a small corral full of colored sheep, probably 20-30. If I run around holding a pair of shears while holding RMB, I cannot keep all of the sheep sheared as they are eating that fast. Sheep seem to eat even if they are uninjured and have wool, but perhaps the 1.1 patch caused fishing rods to damage passive mobs.

So the answer is "I don't think you have to do anything, except expand your flock."

Do not hold wheat in your hand around the sheep - they will swarm you and ignore the grass.

Sheep will also eat tall grass, which you can add to your pasture by using bonemeal. It also has the pleasant side effect of giving you flowers for the renewable dyes.