Hi,
You can do this with Quality of Service (QoS). In e-smith (2.2 kernel based) you should go and use cbq and configure it through cbq.init There was some discussing about this in the forums. Actually I believe somebody already has done it. Even more, we were going to do a "web manager panel" for this but haddnet found the time and we are just awaiting for 5.6 to do it (in our case probably with HTB instead of CBQ as its better and supported in 2.4 kernels ome way).
Regards.