Hi mtngunr!
That's definitely one scary looking dude
without the knife or the rifle. Where did he park his bike?
To answer your question, I suggest that once you have found the proper balance point of the "Thorp" (caution this next step is very important), gently insert the back of the blade in your mouth and bite down hard enough to hold it in place.
Caution! When posing like this, do not react when the photographer says "CHEESE"!
Hope this helps...
Cheers!
David