material overide button toggle on toolbar

how can i create a button on the toolbar that is a toggle state of the “material overide” checkbox ?

been using it a lot testing lights…

i know the script is : renderers.current.mtlOverride_enabled = true or false
but this force me to have 2 buttons.
how can i make it a toggle button?

thanks !

http://forums.cgsociety.org/archive/index.php?t-596860.html