i use a similar technique when people try to stop the roll by basing out, except i try to get on the other side. anyway, that guy should have been focusing more on keeping the opponents head in the middle of his chest, where you get the most leverage for the choke without gassing out your arms. if it slips off to the side, it just becomes an arm-in guillotine.
ive been experimenting with something pretty sick recently with the anaconda choke. if i manage to get an anaconda grip from sprawl now, i just get my weight on my butt by sitting on my heels and push my stomach straight through the opponents neck by leaning back, without having to worry about rolling or pulling guard or anything like that. its similar to the finish with the basic 10-finger guillotine, and it seems to work just as well if not better