i did something similar. instead of using the q.d etc i drilled a hole near where the lid screws in. put in the tire value there.
i also used aquairium grade selastic (sp) to seal the crappy one-way value. the last thing i did use to cut away the hose and and put on 6mm clear tube and a cobra tap. (where sosman put his value) and used a clamp to make sure the beer doesn't leak from the pressure.
But another way (you can kill two birds with the one stone) is buy two ss body washers and use the tyre valve to clamp the two washers either side of the cap to seal the pump hole