Open System Preferences and navigate to Keyboard->Keyboard Shortcuts. Make sure the Full Keyboard Access checkbox is set to All controls. Then, also in System Preferences, navigate toBluetooth and check the box that reads Show Bluetooth status in the menu bar. Quit System Preferences.
Now, when you want to connect a Bluetooth mouse, press ctrl-F8 (you may have to press fn-ctrl-F8 depending on how you’ve configured the function keys in System Preferences->Keyboard). This will set the focus to the right side of the system menu bar and highlight the leftmost system-owned icon (as opposed to icons that belong to third-party apps). Now simply use the arrow keys to navigate to the Bluetooth icon, press the down key, navigate to the Bluetooth mouse you want to connect (I’m assuming it’s already been paired), select Connect in its sub-menu and press Enter. After a couple of seconds your Bluetooth mouse should be connected.
http://mandogmachine.com/2011/05/reconnecting-magic-mouse-using-keyboard/
