Accessing persistant var from another script?

would like to have a button that shows if slideshow is currently running or not.
in the slideshow program there is a persistant boolean variable that can be used.
Is there a way of accesing this variable from a seperate button command or button script ?

ideally something like
@toggle:if Script:"Background Changer.osp"[slideshowToggle]=true
where Script:"Background Changer.osp" is the name of the script
and slideshowToggle is the name of the persistant variable

If not, put it on feature request list please.

You'll find your answer in the vars part of the scripting reference where all types of variables (including 'global') are described.