I had p12 unallied, but my units didn't attack it. I am assuming this is part of the AI, but is there a way around it? I would use p9, p10 or p11, but they have the tendency to stop and come after you, even though they are under the move order.

Create the units under an unallied player, then give them to player 12. You might try player 9-11, then give to player 12, although I don't know if that will work. The p9-11 solution would only work for preplaced units.

p12 always keeps alliance status, and it is allied by default.

Ah, got ya. Thanks.

I was using the player's own units, so I am guessing that wont work if I just unally himself. I'll work it out, hopefully.

Player 12 retains not only the color of the player he is given the units of, but the alliances as well, so you can't set Player 12 to a certain alliance.