I just switched to this plugin from Google Analyticator because of the support for custom variables. Thanks for that feature!
This suggestion is something I'm doing with a site I have coded myself.
Logic: If the X-MOZ header is equal to "prefetch" (normally for Firefox browsers) or X-Purpose header is equal to "preview" (normally for Safari), then don't call Google Analytics.
The bottom line is that prefetched and previewed pages are not true page views, and so I don't want these showing up in GA. At least this could be an option, in case somebody for some reason wants them to show up.
Thanks for your consideration.