Someone asked about this before - is it possible to make it so that if you are in a turret, it's manual, but the instant you leave it, it goes back to auto-fire? The ideal thing then would be to have some way for people to spawn in turrets and move freely between them (by means of 'underground' tunnels or teleportation or something).
I'm still waiting in eager anticipation for the map where I get to man that huge gun in the Endor outpost.
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.