The easiest way to do this is to use a tube cut at an angle where the covering will meet it.

The tube can be something simple and light. Plastic coffee stir stick, WD 40 straw, or from other aerosol can like carb cleaner, Brakleen, etc. Or you can roll your own. Roll a tube of papar about an inch wide and about three inches long. You won't use the entire three inch length but it is easier to work with. roll it pretty tight but keep in mind you will pass a wire or cable through it. Once you have a couple of layers on the tube it is thick enough. Cut the excess length and lightly glue the tube and let it set.

Robert