There are a few glitches in the round robin tourney idea, but I think they can be fixed. I just ran one and I think it did okay.
1) if there is less than 8 people (and more than 4) you'll need to have someone play a 1v1 game since someone will get a bye. Then in the next round play like a normal round robin.
2) If one of the people don't show up, dq them and advance the person in the bracket with them. The other 2 people will have to play a 1v1 game.
Thats all I can think of for now, but I think it can work.