Buy keys like these...
http://cgi.ebay.co.uk/NEW-FORD-SONY-CAR-STEREO-RADIO-REMOVAL-TOOLS-KEYS_W0QQitemZ320224151226QQihZ011QQcategoryZ75320QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
You need 4 - 1 for each corner.
http://cgi.ebay.co.uk/NEW-FORD-SONY-CAR-STEREO-RADIO-REMOVAL-TOOLS-KEYS_W0QQitemZ320224151226QQihZ011QQcategoryZ75320QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
You need 4 - 1 for each corner.