I've got a couple necks I will probably never put frets on and I'd like to take one and make it a slide guitar neck. The fret cuts are already there so I would like to fill them with something light colored so you can still see the separations. What material to use? Some shim stock maybe? Seems it would be a PITA to cut strips that small though. Epoxy? I'm sure it's been done before so please, enlighten me.