self -killing old-fashioned militia in water province for income

[militarist]

I have a lot of militia and need to suicide them somehow.I can't ask my neighbors to let me use their PD, as it will not be accepted.

I have a neutral underwater province I can use, with some tritons there. I want to use a commander with barrel of air.

What spell/tactic would allow me to kill own units, without killing/routing neutral province defence? Foul vapors will not work.Should work UW. UW is, in general, the only kind of province that can turn out independent in the middle of the game

And, maybe simplier question - In one of games I had similar problem with expencive cripped commanders I wanted to get rid of. Maybe some items will help?