Clear vinyl tubing. I cut off a piece with a sharp knife, then use warm water to make it permeable and slide it over the stem.
UDP 3/8 in. I.D. x 1/2 in. O.D. x 10 ft. Clear Vinyl Tubing-T10006008 - The Home Depot - https://www.homedepot.com/p/UDP-3-8-in-I-D-x-1-2-in-O-D-x-10-ft-Clear-Vinyl-Tubing-T10006008/304185141
I once contemplated doing that with silicone tubing. How is the bite feel on vinyl compared to the standard rubber ones?