You can force the assignment of a specific IP address to a connecting client with a specified MAC address using Static ARP and/or DHCP reservations. See:
http://doc.m0n0.ch/handbook/faq-macfilt.htmlThen you should be able to set up Traffic Shaper rules that apply to specific IP addresses.
A connecting client may be able to circumvent this by spoofing another MAC address, unless you can figure out a way to prevent that.