1) Wouldn't it make more sense to allow teams to split bonuses for co-occupying a territory? Perhaps the bonus could be further divided by which team holds at least half of the territory (ex: if the bonus is 3 armies, then whichever team holds at least 50% of the territory gets 2 of 3 armies, or if they have more armies already occupying then the tie goes to them for having a stronger hold on the territory).
2) If that can't be done, then make it so you don't have to "fight" your teammate and lose armies to try and take a territory to get the bonus.
3) Allow the option to "turn over" your armies to your teammate so you can give them territories to provide them the bonus on the next round (perhaps a limit of so many can be turned over so you can't give your team the whole map after every turn and give them a bazillion armies).
4) Allow teammates to exchange cards to help with acquiring bonuses
