[Plugin: Google Analytics for WordPress] Open up Custom Variables for anything

Would be really great if you treated the Custom Variables as you do Page Titles with your SEO plugin. Allow people to pass anything… %%year%%, %%month%%, %%day%%, %%title%%, %%author%%, %customfield[field]%%, etc.

http://ww.wp.xz.cn/extend/plugins/google-analytics-for-wordpress/