You could just load the 280 brass for your intended purpose. Sure you wont get the advantage of the Ackley for a time but there is no reason you couldnt just plan to load and use a load in a 280 case for a bit. After a year you would have a pile of formed brass for next season.
Sounds like a waste of $ to come up with a way to hydro-form brass for really a minimal gain.
Just load them. Work up your load like you would anything else. Then go use it for what it was intended, whether that be hunting, plinking, target shooting or some combination of the 3. When you have a pile of fireformed brass, work up your new load. The first pass through that brass is breaking in the barrel and getting it up to full speed before your final load development. If .280 loads wont be a pleasure for you to shoot, and kill what you need to kill, then the 280ai probably wont either. It does what the .280 does, only a little better.