Below, my original drawing, then pictures of the prototype.
So, the proof-of-concept prototype of the cylinder-handled knife.
It's not what I'd want the finished product to look like–I worked with what I had on hand, and that included a beat-up old butterfly knife and some one-inch PVC pipe and caps. I'd want the blade to be wider, thicker, and I wouldn't have the caps, just a rounded butt and some kind of guard; however, it does give me enough of a feel for the design to tell me that it will work like I wanted. Proportions are off, I'd have the handle be a inch or so shorter, too, but there you go.
The knife's handle fit snugly into the pipe, and I cut slots at the top for the tiny guard that flares a bit at the base of the blade. With the knife pushed firmly in place, I cut a slot in the top cap for the blade, squirted a fair amount of epoxy into the handle to set everything, glued the caps on, and voila! It doesn't have to work, save to see if I can manipulate it.
I'm sure a knifemaker could produce something ever so much more elegant.