I've seen it done, but anything more than just a slight tweek is gonna be really really difficult. It seems like there would be pretty much no room at all for error.
H Yule, I have the same situation that you do, and it is possible to do things like a titled indy, but theres not alot of air to work with obviously. Last summer I remember someone had a forum about doing tantrums behind a seadoo and they were able to do it. It also helps if you have someone with some weight sitting on the back of the seadoo (call it "ballast" hahaha) to make somewhat of a bigger wake. When your riding behind a seadoo, any kind of weight helps.
I saw a video on youtube yesterday of a guy doin' tantrums behind what looked like a john boat. Had an outboard motor with the handle slash throttle attached. Looked for it later to show my wife and was unable to find it again.