Dear John,
In reading your post a couple more times, I think I see what you are after. Elaborate a little more on what you want exactly. You want the NIC to get an addy from the dhcpd server from the Subnet A address pool and then want to also obtain an addy from the Subnet B Fixed addy pool so the clients nics has two Ips? Correct?
The client can just connect to two networks handled by the DHCP server (on different NICs of course ;))
On Subnet A it should receive a dynamic address within the range and on Subnet be it should just obtain the address defined in it's host declaration.
This I am not sure can be done with dhcpd. However you can specify NIC to fixed static addys and the nic harware address in the dhcp.conf file.
How does that work?
Best Regards Marcus