I guess you could vent the air back into the room but remember the Pc will be creating heat, therefore your ambient temps would not be as low.
On the other hand if you forcing the cold air out of the room at a higher rate, the room would never cool. You'd be sucking in warm air from adjacent rooms.
Scrap that idea.
The best suggestion would be to just to force as much cold air through the case as possible. If I were as crazy about low temps as you seem to be, I would remove my side windows and put my PC in a box-like device with an open bottom and attach a window fan to the top like this.