If you cannot configure your router to do what you want, I recommend taking a look at Smoothwall, IP Cop or something similar. You would also be able to physically separate your wifi traffic from your wired traffic quite easily. I don't think I've seen any consumer grade routers with that ability but they may be available.
My Asus RT-N56U has the settings for QoS also does dual wifi so the N traffic does not get slowed down by lower speed traffic on it.