Well Ronster what I did was remove the nozzle completly and goop a CPVC coupler directly onto the valve. It wasn't a perfect fit with the case but I just used hot glue around it all so it wouldn't wabble. And yes, for the purposes of gooping the vinyl tubing onto the pump and the valve it is the same as the shotgun mod. (glad to see some people actually appreciating and using my contributions)
Ronster, my best guess would be the first one (the one on the left). Just try to figure out where the air is exiting the pump (to fill the chamber) and chop just after that. Lastmanalive, adding the pvc for an air chamber would make the gun require many more pumps for the same range (with that much more air, the dart with have already left the barrel), so it would negate the whole purpose of the mod.