BetterTouchTool, 10.8 and Magic Mouse - trigger Notifications

Have you looked into Keyboard Shortcuts for Notifications and if one can be made for that, use BTT to make a gesture for it, then apply the shortcut in System Preferences > Keyboard > Keyboard Shortcuts.

Also know, that with a descriptive thread title like "BetterTouchTool, 10.8 and Magic Mouse - trigger Notifications" you could get a knowledgeable audience.
To edit your thread title, click the EDIT button, then the GO ADVANCED button and see, where you can change the title.