just use your team to cut off the map. Have a team mate in all the spawn locations except one. Stay around 20-50 feet from that location and just pick them off when they spawn. Its pretty easy to do on most maps.
Wasteland is the best because you can force them all to spawn in the cave and then just pick them off whenever they come out or just rocket in and make their day suck really bad
This can work in all gametypes, my clan uses it often in TDM and HQ. Not on purpose but we spread out and watch the map and each others backs and generally it leads to them being spawn trapped, and its not like were just going to let them out cause we feel bad :p