Unfortunately, I don't think you can. When logging into a pc, it MUST have a valid IP address to communicate with the server in order for the credentials to be verified in AD. Remember, DHCP allocates an IP as soon as windows starts up on the client pc. One way to do it is to make reservations in DHCP based on the MAC addresses of the pc's that connect to the server and set the pool size to the number of pc's that will be in use.