Many thanks, brilliant responses
This board is the bees knees, or rather, it's contributors are
I never thought of a software solution, but with that mention, I went to Google with "Bandwidth limiter utility" and got
http://www.softperfect.com/products/bandwidth/ , which, as suggested, can be installed on clients but controlled by the admin. If a client deleted the utility, the admin would know.
Only snag - you have to input the rule every time the client is booted, or pay $99.00 for the full version.