I found this idea in the N64 game "conkers bad fur day"
you can pick 2 teams..be the escapees running up and have to make it past enemy fire of the bunkers and have to make it to safty under the bunkers,the bunker holders are equiped with LAW and a barret...they try to make sure noone gets past the bunkers...anyone have suggestions to this idea?

You can easily simulate this 'game mode' with some creative mapping. Heck, you can go play inf_Invasion, that's virtually what you're asking for.