If he has no interest in theory, don't try to force it on him, he just is not going to care. Or worse, he's going to be reluctant to jam with you anymore because you are getting frustrated that he won't learn what you learn. (Screw Rick, he's gettin' to be a drag, man! :D)
You didn't really indicate, when you are doing your thing and he's doing his, if you are in key, or it sounds ok or sounds like crap or what.
I might suggest not doing anything original. Instead focus only on jamming some songs written by others, that way there is no need for debate on what key, what scale, whatever. It is what it is. Maybe choose songs along the vein you are interested in (like something that uses A Harmonic Minor?).
Over time you can maybe say 'hey look I wrote this thing, lets try it...' then gently lead him into the bass lines you were looking for in it. Still no need to teach him theory... That kind of thing is like leading a horse to water. :)
...so ever since then, I always hang on to the buckle.
