Icy Mike -
jehiah - This is done in BJJ, not sure why you would think BJJ people would say it "can't be done"?
I have seen it done using the gi skirt and the knot of the belt, from x-sides, N/S, basically any Kimura setup.
In answer to your question, the most common choke is a collar choke with your free hand inserted palm down into the far collar, then dropping your elbow to the mat.
Thanks. I use a lot of hyperbole if you're not familiar. If anything they will probably say the scrubby, forced setup is no good.
But as for the collar grab you suggested, that's actually what I've been looking for is far side collar. I just haven't had any luck with that. I will keep trying though.
A couple tips that may help with getting the insertion on the collar:
Pressure on the gut/hip area tends to get people to lift their head slightly and/or not pay proper attention to their neck. This can be done a variety of ways, obviously, but the principle is the same.
Slack and deception matter. This is another example of the principle "smooth is fast". I often see people stabbing their hands around at collars, or a taking away the very slack they need to setup a collar choke. Once this is done, the opponent is aware of what you are doing.
This may sound like excessive analysis, but really it's similar to using striking the head to open the body, and striking the body to open the head. It is hard to defend both at the same time, but the timing has to be deceptive, natural, and smooth.
So, pressure his body and/or that shoulder, knowing that you want the far collar insertion...IOW, I wouldn't combine that particular choke with the knee on neck as his attention is already up there on his neck, and the slack will almost certainly be gone.
I know that's not a lot of specifics, but I think those principles will work well for you.