I don't know if the game is actually already taking that into account in the mechanics...

But, as I understood it, to maximize manpower you are supposed to use chain gang program on the last pop in the system, right? Else that food would be wasted when the system is full, as only 20% go to manpower, if I got that right.

So if that is the case, shouldn't the game automatically do the chain gang programm effect once the system is full and you could get a new pop (theoretically)?

Or is there something I didn't quite get right?

well, the chain gang program - as far I understand it- wastes your system's industry for the turn. You are supposed to send population from nearly or totally filled system into systems wih alot of space, also their an era 5 tech of the diplomacy sector that turns exec food into industry.

Oh, totally right, I didn't take industry into account as a factor. 

I guess I just got a bit annoyed by the repetition when using it on a large scale, as you cannot queue it multiple turns.

Chain gang now works even then it is not first in build queue. Dont know is this by design or bug.