What I did in the first tourney when I needed random seeding was just an updated Version of the hat thing. I wrote all the names down and assigned them each a number in the order they joined. Then I did a search on google for a website with a random number generator. Found a ton of them. Anyway I picked one that would give me a string of random numbers between 1 and n and, violin, random seeding.
For that matter you might be able to find a shareware program that will take your names and generate a rondom bracket for you.
Course the hat thing works fine too.
The main draw back to the pure one on one tourney is what happens when a player drops out. I guess his opponent would get a free pass to the next round. Of course it's all random and it's all for fun, so even if it happens maybe noone will complain about it. Hopefully not anyway.
Geoschmo