set site-id in cookie

I am using Piwik analytics tool. I need to add site-id to the cookie that is being set by Piwik. Any i开发者_如何学Cdea, how to achieve it?

You could easily modify the piwik.js to customize the data you put in; see the code around http://dev.piwik.org/trac/browser/trunk/js/piwik.js#L1370