I used some foam pipe insulation from the hardware store to create handles for doing parallel bar dips with two barbells. Cost $1.50 for 6' of it, and I used maybe a foot and a half. Label says 'fits 3/4" copper, 1/2" iron'.
There's also higher density rubberized pipe insulation.
This will make the grip thicker, but the foam will compress. For dip handles, it's fine; much gentler than the bare barbells. Would probably work decently for OHP and curls too. Definitely won't work for deadlifts.
But... for less than $2, you can find if it will work for you or not.