Is it possible to compromise with Aizen?
On a purely geopolitical level, Leaf is his best option for an ally. In terms of legitimacy, support of the Pangolin Summoner would completely solidify his reign. Opposing us, even assuming he wins, will cost him greatly. We have a lot of leverage over him, especially given this is a life-or-death matter for him, whereas we can afford to walk away and live. I think we could get a lot of concessions from him in return for pledging not to undermine his authority anymore.
The real question would be whether we think a better Isan is possible with Aizen still at the helm, and whether Keiko and Yuno can accept it.
Honestly, I'm afraid that whatever clever plan we come up with is going to, even if successful, ultimately result in violence and leave some of our people dead. We've had a lot of close calls throughout the quest - eventually we're bound to hit a bad beat at an important juncture.