It doesn't last long. My DD only did it for one night but I reckon the longest you'll have to put up with it is a week or so before he works out what to do. I'm jealous - my 10 month old still isn't rolling and wakes because he wants to be on his front and can't turn himself round!!
I put my DS in his grobag in the day while he was playing so he figured out how to roll back! It took a few days, now he flips about all night like a worm - watching him on the monitor is better than tv!