Do you have only the Linksys router between clients and Internet, or do you also have a Linux box between router and Internet?
In the latter case it could be done easily, check out the
Advanced Routing & Traffic Control Howto.
If you have only the router you might be able to
replace the firmware (I think it's only possible on the Linux-based model -- has an 'L' in its model name somewhere) in order to be able to fumble around yourself.
(Just getting some cheap Linux box to put behind the router would probably be much simpler)