I'd see if you could find an o-ring. Baring that, very carefully and evenly go around the spindle (which does look awesome) with black electrician's tape. Once the thickness is just right, it might simply fit there no problem.
For best results I'd drill a hole, tap it and hold it in place with a set screw. It sounds daunting, but I just started tapping and it's a lot of fun and super-satisying when it works.