This is what I encountered in my last MV game. I couldn't get the last AI to surrender their last planet in exchange of a peace treaty because of a big "-- they don't trust us" diplo hit (as I've previously attacked them for 2 times). Instead, I gifted them my treaties, and was fastly "close" in relationships.
When then the Alliance was offered to the Krynn they even went so far as to hand me their FlagShip, an Influence StarBase... and their last planet. Actually, I could have had those +39% Influence Resource Mines as well, just needed to de-select another base. I think that this is the only way how one could trade for Starbases or the Flagship, as swindleing doesn't work (ships are screened out during a war).
The bargain actually did end said game, as it was the last AI. It did count as Military Victory, although I can't say if this would be counted as an Alliance Win (had it turned off at the game's setup).
