Just use rcon, you can then ban the guids by searching for the player name, it should keep track of all players that have joined so you can ban them after the event. It should also allow IP bans. Just keep rcon running on the dedi box 24/7, you could even run it on your home PC if you wanted as well.
Follow up to Witcher, user this
http://battlewarden.net/
Probably the best one out there.