change default http port using DHCP - No WPAD - No DNS

Hello everyone,
I need an option in DHCP that would change the default http port from the
default port 80 to an other port number. When the user leaves my network and
get a dynamic IP address from an other network, his default http port 80
should be back to normal.

I am not looking for an Active Directory policy where I can change clients
ports. My users are public auditors and have no access to AD.

Any help is greatly appreciated

Thank you
Mike