I thought an eraser could work well as a rubber tip but it didn't turn out as well as I'd hoped. Still neat though.
This uses an eraser from a Ticonderoga NO.2 Pencil. Cut it from the base with a razor and slot it into the performance tip. Make sure you slot it in with the rounded end facing outwards. A dot or two of super glue in the tip is recommended but not necessary.

If the tip breaks, it has a hole through which you can push out the eraser and use it for a new one.