Simple way to throttle bandwidth to certain websites?

I have certain users who spend way too much time on non-work-related sites (such as Facebook).  Blocking those sites completely would raise thorny issues that I'd rather avoid.  My preference would be to implement some simple system -- preferably right on the client PC (running Windows 7) -- that would allow me to throttle bandwidth on a site-by-site basis.  If I make it sufficiently painful to view Facebook, or if YouTube videos keep buffering repeatedly, maybe people will eventually stop trying.

Yeah, I know you can probably do this by implementing QoS on the router, or setting up a proxy server, or some such thing, but I don't want to go that route.  I'm hoping for something that can be done locally, right on the Win-7 machine.

Thanks.