Block clients without a specific identifier from DHCP server

Is there any way to stop clients being issued an address by a DHCP server unless they have a specific identifier ? MAC addresses are impractical because there are several hundred clients involved. Specifically I want a DHCP server to offer IP addresses to mitel 5330 IP phones and reject requests from PCs. Is this possible ? What is the best way to do it ? Creating a seperate VLAN for the phones would be one way to do it but the current setup makes that a non trivial exercise. Can the DHCP server in the mitel 3300 ICP be configured to do this ? I know the phones only accept IPs from DHCP servers configured with the correct string so surely the reverse is possible. Any suggestions welcome.