Single elimination "byes" have been added.
And it works just as I think it should work.

By the way, it works only for tournaments created after the time of this post. The tournament creation form now allows to specify the minimal and maximal value of the number of single elimination tournament players.

For instance, if you create a tournament with minimal 4 and maximal 32 players, and 10 players actually sign up, it will be created as a 16 players single elimination with 6 initial byes, assigned to top rated players.