I dont see much hope of gaining entry to the Ideal holder but there seems to be enough of a lip to rig an external strip of felt or velvet.
That is why I prefer the double sided holders used on Favorits and Juwels as they are bolted together.
Have you tried leaving the dark slides out for a while and trying to ruffle up the velvet. If it is missing you might try to introduce (poke through) a piece with glue on the back and then trim it flush.