Once you complete the holder, you can hotglue the actual caps into the holder so they don't go missing.
I think this could be a very useful project for an art station. While I was poking around at a new-to-me blog, One Inch World, I found a very informative post on refreshing these sorts of dried out markers. I haven't tried it yet, but you can check out the tutorial here.
Have a lovely day! This post is linked to