Hey danandteri,
It makes sense, and I know what you're talking about. However I still think you should learn the songs first. You can't accompany something, if you don't know what you're accompanying. I don't know if that's the right way to put it or not. Let me try again, and maybe this will make more sense.

The patterns you refer to are not that difficult to learn, if you know the song. They're probably what's called sus chords, and other positions of the triad. He also used a capo on a lot of stuff, while another guitar played the rhythm. Knowing the song, and the rhythm will make it much easier to figure out those patterns.

I often have students that want a shortcut, but I advise them against it. They want to learn this riff, and the leads to a song. They don't understand until after they learn the rhythm, how it all fits together. I think it would be the same in your case, learning the chord progression and the rhythm will let you know how to accompany the other guitars. In some cases he just played a pattern around the basic chords of a song. If you don't know the progression, it's hard to even know where to start. You can do what you want, but I would learn the song first. I recently heard someone say, that you can't embellish something if you don't know how it goes to start with. I hope this makes sense to you, and you can always take shortcuts after you go the long road.

I just saw your reply when I got in from a performance, figured I would respond while winding down. What you want to do will be much easier if you know how a song goes. It will also be easier to apply it in other songs, once you get used to it. I know this isn't what you were hoping for, but I hope it helps you a little bit.