If in your opinion it wouldn't look drastically out of place, you can always try EvilMike's method from the Fortress of Decay (devres71.j2l) and kill the player from time to time with a special CTF bases system. The only side effects of it are losing all the collected fastfires and necessity of making the level a bit more linear and one way, as you need to pass through certain "checkpoints" and can't come back.