All you need to rebase tac nukes (which are better in this context no matter what, reduces the potential stupid ways an AI could use a nuke, although Rolo is saying you can't rebase ICBMs to AI's i've not tried it...)
is open borders. They don't even have to like you other than that. They'll gladly take the nukes and any diplo penalty for firing them off. Neither side seems to be aware of this arms supply, which is really convenient

.
If you have good nuke production, you decide who wins a war, if anyone. Remember, if it gets one sided you can always hand them to the other side

. You do still have to find a way to win yourself however. Usually with that kind of tech it's domination, UN, conquest, or space.