It can be done. You would cut a small hole in the tubing for the filter and then use aquarium silicone to attach the CO2 tubing to it. The only thing is that this is permanent and you can get a large air bubble in the impeller which could stop the follow and destroy the burn out the motor. I wouldn't do it.
My suggestion would be to make or buy a CO2 reactor like what is in the DIY forum. It explains how it would be attached and everything in the sticky.
Alternatively you can attach an air stone to the CO2 tubing and put it below the intake of your filter and let it run through the filter like that. Many people do this but I think the best way with the most efficiency is the reactor.
Depending on the size of your tank you can also us a Seachem Reactor 500 system. There will probably be many more suggestions but these are mine, hope it helps.