Segments are usually typed into the URL.
If you want to check it more often it would probably be best to code a widget showing the graphs already using segments (as I don’t think you want your regular graph to not anymore display the usual data), but as I already implicated, that’s only the starting point I can provide you.
Happy New Year! If you are still using Piwik and interested in the awesome new feature of “Creating a Custom Segment in Piwik and apply to reports in Real time!” we need YOUR help, with a little or big donation at: http://crowdfunding.piwik.org/custom-segments-editor/
This will allow to dynamically add or edit, a new set of rules for example “Show all visitors from USA and using Firefox and using Google”. This will be done via a simple to use interface. See screenshots and more info here: http://crowdfunding.piwik.org/custom-segments-editor/
We are crowd funding the future of Piwik and this feature in particular. With your help we can do it.