Increase number of available ip-addresses

Hy, (note in advance: my English might be a bit, well, rusty...)
I'm using m0n0wall mainly with the Voucher function. I understand, that 
the number of available ip-addresses given by the DHCP-Server is 
limited. Nevertheless, I have been asked, if there was the possibility 
to include more than 250 ip-requests. (Don't ask me about the sense...)
The only way I could imagine, is, with allowing my WLAN-Access Points to 
set up their own subnets and route to the m0n0wall instead of passing 
through the adress-requests from the clients.

Would there be another possibility (e.g. with more subnets dealt by the 
DHCP-service of m0n0wall itself)?

Best regards, Ralf.