A really good example of using the 7 button like you're talking about is the French Two-Step on Ray's first album For Old Times Sake. If your curious about what he means that's a good place to start listening. It's a relatively easy song to learn and the "Chanka-Chank" on the 7 button is pretty obvious. I'm not going to try to explain in detail how to do it, I'll save that for Ray, plus I'm far from being a qualified accordion instructor.
However, I will say that not having that "Chanka-Chank" sound is one of the things that keeps your playing from sounding Cajun and thats what a lot of begining players (myself included) struggle with. They can play the notes of a song correctly, but something is just missing. It doesn't really sound Cajun and it doesn't have that "make you tap your foot" two-step rythm. The good thing is that once you start getting it, it's a whole lot easier and cleaner than putting a lot of triplets and frills in a song.
Perhaps someone with video could shoot the part of the class that deals with it and get Mr. Abshires permission to post it on Youtube for the folks that cant get there.
Thanks,
Greg