Safari Extension, Fluid App

I've written a simple extension for Safari that captures clicks on the RSS button in the address bar (calls to the feed:// protocol) and redirects to Google Reader instead of Safari's feed reader. If, however, the user has a Fluid app (one that opens Google Reader) set as their default 开发者_如何学Gofeed reader the intercept doesn't work.

Is there any known way to capture a request that's being sent to a different app? The extension currently keys on document.beforeload(), but if the document is being opened in a new "app", it's never reached, of course.

Is there a different event I can catch? I haven't found a comprehensive list of events that extensions can catch.

Thanks.

Extensions are a part of Safari not webkit, so safari extensions aren't available in other apps that embed webkit (like Fluid).