How to unset vendor specific info on a per subnet basis?

[Michael Carpenter]

List,
I have a config which sets vendor specific information for all PXE clients
as shown below. In one particular subnet I want to remove these options from
the lease for clients of this subnet only. Is there a way to do this? I have
tried to use the unset statement with no luck. Can I make my "match if"
statement more specific? If so, how would I identify these clients based on
their subnet?

# extended PXE option 43 declarations
option space PXE;
option PXE.discovery-control code 6 = unsigned integer 8;
option PXE.boot-server code 8 = { unsigned integer 16, unsigned integer 8,
ip-address};
option PXE.boot-menu code 9 = { unsigned integer 16, unsigned integer 8,
text};
option PXE.menu-prompt code 10 = unsigned integer 8;

# Clients which are PXE booting will be placed in this class
class "PXE" {
        match if substring(option vendor-class-identifier, 0, 9) =
"PXEClient";
        option vendor-class-identifier "PXEClient";
        vendor-option-space PXE;
        # suboption 6 (PXE_DISCOVERY_CONTROL); a value of 7 tells the client
to use the list of PXE servers in suboption 8
        option PXE.discovery-control 7;
        # suboption 8 (PXE_BOOT_SERVERS); format is [server type (2 bytes)]
[# of servers (1 byte)] [server IP (4 bytes)]
        option PXE.boot-server 6 1 9.42.106.51;
        # suboption 10 (PXE_BOOT_TIMEOUT); tells the client how long the
boot menu should be displayed
        # we are setting this to 0 secs so that the first menu option is
seclected immediately
        option PXE.menu-prompt 0;
        # suboption 9 (PXE_BOOT_MENU); format is [server type (2 bytes)] [#
of characters (1 byte)] [boot menu title]
        # the boot menu title is required, but will not be used since we
chose to boot the first choice
        option PXE.boot-menu 6 14 "RDM Local Boot";
        # See also http://www.rembo.com/rembo/kbase/kb01102802.html
}

-- 
Michael Carpenter <macarpen at gmail.com>