Hi Yoda,
I'll check out pnf. I'm glad to hear about it.
But I don't think it will help significantly with Kechari. The frenum, which is a tendon, not a muscle, is the real limiting factor in tongue extension for kechari.
If there was no frenum in your tongue, at the rate of the stretch of muscles, I think you would get all the way to stage 4 in a month or two...
Tendons, on the other hand, almost don't stretch at all....
-D