You can switch them on off from any position(f.i. pilot seat), anytime.

That doesn't work when you allready have a substantial workload flying the bomber and trying to evade enemy ... there has to be a command or something gunners have to be a bit more inteligent (no x-ray eyes though :P).

A little less A and a little more I would probably do the trick here. A properly trained gunner would (more or less) hold his fire until the target was in range and/or he had a good shot, if they have pulled that off, then things will be good. (and dangerous)

This could be done the way it was in silent hunter 3.

Available gunner modes:
Fire at will
Start firing at long range
Start firing at medium range
Start firing at short range
Cease fire

You could totally silence them if you wanted to sneak past, or tell them to fire only at short range when it's clear that you've been spotted and it's time to defend yourself.

Alternatively, when flying heavies up high and you know you'll be spotted anyway, you could tell them to fire at long range in order to deter the fighters from getting close.

'Number three, you're in my way...I've got him in my sights' as a command.

...and then he obligingly pulls away.

Would be nice.

Or how about they don't fire at burning aircraft headed for the ground....aircraft the you the human set on fire lol.

Gawd I hate that.