Getting a full list of custom variables

I want to fetch all the custom variables and its values assigned to an idSite.
Does PiwikTracker for PHP provide me this functionality?

For example,
There are 5 custom variables assigned to idSite 25 with scope as page
I want to fetch all the data of custom variables regarding idSite 25. is it possible?

Or probably other way to look at it is,
I want to fetch all the data of idSite 25, then extract the needed custom variables from it?

How to do it? Please guide

EDIT - Apparently, the documentation says, it returns the currently assigned custom variable. Does this mean, we can’t get a full list of custom variables that occured within idSite 25?

Thanks