He can just keep on riding those wide knobbies. Might take a few tires but eventually the chainstays will wear in exactly the right places and he will have the clearance he needs. And if Larry is a light, smooth rider that is kind to bikes he might get a year or years out of the frame before the chainstays snap. (I've broken several chainstays on steel bikes very close to there. Not a big deal. Don't know what it is like when it happens on a carbon bike.