- Duplicate the Google Notifier application.
- Select the duplicate, control-click on its icon, and choose Show Package Contents from the pop-up menu.
- Navigate into Contents, and then open Info.plist in an editor.
- There is a property in that file called CFBundleIdentifier, with the value com.google.GmailNotifier. Change the property's value to com.google.GmailNotifierMysociety instead.
- Save your change and quit the editor.
To solve that, you'll need the Developer Toools installed. If you have them, inside the Gmail Notifier app (the copy you made), open Contents -> Resources -> English.lproj -> MainMenu.nib with InterfaceBuilder. Double-click on the BothMenu item and add an Item object at the end of the menu, and input myname@mysociety.com. Save your work, and you're done.
[robg adds: This hint replaces this older hint, which as the commenters noted, will not work across restarts.]

