dhclient.conf: Send 2x host-names to the DHCP server?

Solution 1:

Why not have two IP addresses on a single client interface and send in two DHCP-with-hostname requests, use a reservation if you want to be consistent. Obviously it's a waste of an IP but it should work just fine.

Solution 2:

Unfortunately the DHCP protocol does not allow this. The hostname is set via the Host Name Option - see RFC 2132 Section 3.14:

3.14. Host Name Option

This option specifies the name of the client. The name may or may not be qualified with the local domain name (see section 3.17 for the preferred way to retrieve the domain name).

Sadly you can only have one entry per request, so Chopper3's solution is probably the only way.