What about incorporating a player speed rating?
Each player would have a speed rating, e.g. between 0 and 100, 0 being infinitely fast and 100, playing at the time limits.
The rating would be calculated and averaged for each move made as follows:

Time Taken per Move / Time Allowed per Move

and added to their overall rating:

(Total Time Taken per Move - Total Vacation time used) / Total Time Allowed per Move / Total Number of moves

For tournament creators, they could add a minimum required speed rating.
For the entrants, the pending tournament could also display the speed rating of the slowest player, so they have an idea how quickly it may progress.