Glider Capo for Guitar

A Glider Capo (Slide Capo?) allows you to slide capo position in the middle of playing.

This is useful for songs that raise key in the middle.

Here's a comercially available glider capo in action:
https://www.youtube.com/watch?v=Bo__FVbZSww

My design can do what the video does at 0:33, but has a bit difficulty in doing 0:16