Nice work on this plugin - the graphs look great and the documentation is easy to follow.
I have not looked at the code yet, but I'd also like to tie in variables to create graphs on the fly. Doesn't have to be directly from the database - just being able to define variables in PHP and then call the plugin would be great. It may be possible to do this already - I don't know much about how shortcodes actually work on the backend...
Cheers, DK