xmas is soon: Now I would not think it would be too hard to put some sort of by system to work with less people.

lets say it is a 16 player single elimination tournament, and only 12 sign up.

Round 1: 16 players (with 4 of them "ghost" players which randomly get put into the tournament and automaticly give the person who played against them a free win/by into the next round - of course does not count as a won game - just a win into the next round of the tournament. - so 8 players advance.

Round 2: 8 players start, 4 winners

Round 3: 4 players start, 2 winners

Round 4: 2 players start, 1 winner!

So that is why a single elimination tournament needs to be to the power of 2 (2, 4, 8, 16, 32, 64, 128, 256, ...) = and does not work with a multiple of 2. (2, 4, 6, 8, 10, 12, 14, ...)

Edited to add: Of course only do this with the 8 & above single elimination tournaments where at least more then 1/2 of the players sign up. So if you set up a 32 player tournament and only 15 sign up, then it should be reduced to a 16 single elimination tournament with 1 "ghost" player to give a free by.