Here is an helper I made to do a progress bar some times ago: http://www.html5gamedevs.com/topic/40142-can-we-customize-the-look-of-babylonjsgui/?do=findComment&comment=235200 .
It is working a bit better than just a slider. It probably can be improved to used ninepath images. For now, I am using two rectangles, a container and a text block.
You can find the code to run it just here: Babylon.js Playground
EDIT: I updated the link as it was not working for some reason.