You can configure QoS on the 1242AG, but your infrastructure switches and L3 is the one that will need to be setup to keep the QoS markings and your L3 can do the rest. How to do per user and per COS.... don't think that can be done without a lot of headache.
You can't do that on the AP... the only thing you can do on the AP is QoS markings... take a look at the link I posted. Whats a headache about it is how are you going to determine what user... by ip or mac address? I can see if you want to configure this by subnet mapped to a certain ssid on the AP. If you really looking for how to do this, I would post this on the route/switch forum. I have never gone that far as per user. Sorry.