I've been using this Pentel 8500 for a while now. I carry a pencil in my pocket at all times, and I'm impressed with its durability and ability to resist snapping under all the bending that a pocket pencil goes through. It fits the "thin pencil" requirement, but the plastic barrel is just a wee bit slippery, and I have a tendency to let it slide out of my hand when I'm not paying attention to it.
Time to fix that!
Step 1: Stuff
-Pencil. Surprise, surprise. Or a pen, I suppose, but I only use pens with caps, so this wouldn't really work.
-Sugru. A 5g sachet is more than enough. Pick whatever color works best, I used black on a dark green pencil.
-Alcohol and wipe of some sort. If you've used the pencil before, it has your finger oils on it.
-End effectors. Hands work well if you have them. If you're a robot, try a grapple or grasper.
-Work surface. The residue seems to wipe off my desk without a problem, but for rolling it out I put down a piece of glossy paper. Waxed paper, aluminum foil, plastic wrap would probably work equally well.