this may have been posted already, but I was visiting a planet that had a very large ape city, so I decided to spawn the first boss right in the middle of it, low and behold the apes killed it in about 2 mins with minimal damage to the city itself. I just sat back and watched, then collected the loot. Maybe bosses should insta-kill npcs or something?
Actually, I wouldn't call that an exploit any more then building an arena to fight the boss in. You're just using terrain to your advantage and the UFO boss is the weakest one. I see no reason why you couldn't use your surroundings in a clever way to defeat it.