Actually, I've been considering how to do this for my next app.
Not split testing the sale price though, it will be free. (It's just too hard to get people to buy an app outright) I want to split test in-app purchases. I think this should be fairly straightforward to implement. The only downside is in the app store 2 different items would show as top in-app purchases with different prices. People might be upset about that, but I doubt anyone would notice.