In the shotty room in Chill Out, there is a pillar by the flag spawn that you can get up on. Just nade the overshield by it. Throw a plasma, frag, and rocket yourself up as you grab the os. Hopefully, you'll make it. Controlling that room can be pretty big, and that pillar gives you a great view of the room. Not to mention few people will expect anyone to be up there, or think it's impossible to get up there. If you go up there, though, try to bring up quite a bit of ammo (definitely bring a pistol. Or Sniper rifle).
Hope this helps. :)