You should be able to form 40 degree shoulders directly, without having to resort to things like COW fireforming. I do 35 degree shoulders directly. Making them 40 degree shoulders would be one more step. The trick is to bump the shoulder back with progressively smaller necked dies that have a 20 degree shoulder. Using progressively smaller dies will help prevent puckering at the neck-shoulder junction.

7mm Kraken case forming
I also shoot 6mm Crusader, which is basically the same as 6mmAI, but with a 32 degree shoulder.
Here is my method:
1) Anneal the case down to where the new shoulder will be.
2) Lube the case up and run it into a 308 Win die. Adjust the die to put the body-shoulder junction where it needs to be in the new case.
3) Repeat 2) with progressively smaller dies that have a 20 degree shoulders (7mm-08, 260, 243, for example). Trim dies work well, or buy cheap used sizing dies and chop them down if necessary...
4) Anneal the case again once you get to the desired neck size.
5) Run it into the final sizing die with the final shoulder angle. (I would use a die with a 30 degree shoulder at this step for your AI, maybe even a 35 degree shoulder die, then do another step with your AI die).
You end up with something that looks like a factory case. Shoulder is even a bit sharper.
A lot of steps? Yes... but I still find it a lot faster than blowing out the cases with COW. Especially since I can do it at any time (read 1am when the missus is sleeping) in my reloading room. Goes pretty fast on an XL650...