depends. if you control the modem pool, routers, dns, & firewall then yes.
make sure the router for the modem pool only allows connections to the web servers you want to use and to the dns server.
setup ppp on the modem pool to use your dns server.
setup the dns server to resolve www.onlyme.com. for any other dns request return an ip that takes the users to a page with the error that says they have no internet connection, please contact the isp etc.