I wanted to include this in the feature request section, but actually plan on trying to implement this myself and submit the code to the m0n0wall team.
Before I did though, I wanted to get some feedback in case this isn't even possible before I start.
I know right now, you can setup a reservation list by MAC, or you can restrict if further with the "Only respond to reserved clients listed below" option in DHCP.
I wanted to add another section that is similar to "
Don't respond to the clients listed below" option. The logic behind having a strange option like that there is allow me to stop assigning IPs to virus infected/spewing machines for a while until they can be located/clean and also help to locate rogue DHCP servers running on the network that have un-managed switches.
Now I know to start here on my research,
http://www.isc.org/sw/dhcp/ but if anyone has already read up on the DHCP server and know this isn't possible, please let me know now.