this isn't really a real solution…but what i do is use a single headless linux box for all torrent downloads....you could do the same thing and then do ip based traffic shaping....my client of choice is torrentflux which is web based so i have the added pleasure of being able to add torrents from anywhere with a internet connection. I then use samba to share that box with the network.
i THINK utorrent now has a web client as well so if you hate linux that's always an option....like i said, it's not a REAL solution to your problem but for me, i've found it much nicer because it gave me a good use for otherwise useless junkpile hardware.
if you have a computer sitting dusty in the corner it might be something to think about....even a p2 or p3 would be fine