I can't say that sounds like a good idea, but can't think of any reason it'd do harm. The two things I can think of that it would do is wash and de-grease the belt, and to give it a good heat cycle. I would be careful of what you use for soap. I've always scrubbed my new belts with plain dish soap and hot water to remove any grease or mould release agents. That might be an old-timer idea, you'd think they'd send them out pretty well cleaned, but it does take care of any grime from handling and shipping. It's definitely not a substitute for recommended break-in though. As I understand it, the two big benefits of a proper break-in are that the heat cycles help stabilize the various compounds in the belt, and running the belt up and down the clutches scuffs the belt to its intended surface finish.