Client access license reservation

i am setting up a system to have a win2000 server with terminal services and 20 clients via windows 2000 machines. i have a 15 user license for the server and the terminal services licenses are covered by win2k pro. i have one user( the 21st client)who is going to purchase access to this machine but i need a way to reserve one of the CAL for him leaving 14 for the other users to use.( they don’t use even that many at this time). due to cost restraints i can’t upgrade the server license at thistime( it would have to go up another 6-10 users which may happen in next years budget, or not depending on number of denials