That connection also has a little plastic prong which I believe serves a function, so it's not just a matter of getting the right size connector.
I'd suggest contacting Champion and ordering that entire assembly with the pressure regulator and then removing the pressure regulator and installing a connector at the non-generator side of the hose. Once you've done that, report back here with what you did so I can do the exact same thing! ;-)
What I've done instead is bought a Y connector propane device and extension hose so I can connect the generator to my RV tanks that way, rather than use the quick connect under the trailer.