Stu, I had a look at the game files and I extracted some of the map information, and I made this extremely accurate diagram, took me ages it did.
The green line represents a metal gate, if you close that and stand in the corner next to it (where 47 is shown), then the 48's should all follow the blue line and come out the red door. It makes it as simple as simply clicking the LMB when the door opens. (iirc, there is a way to keep the minigun spun up so it shoots instantaneously. I think if you just tap the button, it spins up without shooting. I may be wrong though)
If you go to get the minigun, then there will be one clone loose by the time you get to that spot, but he shouldn't be much of a problem.
Also, the worst missions are the Columbian mission, although my least favourite missions in the series as a whole are the Japanese missions (outside) in SA. They are absolutely awful if you're trying for a Silent Assassin rating. Guards should not be able to recognise someone as an intruder from 50 feet away, through blinding snowstorms, while they're wearing a guards uniform that literally covers every square inch of skin.