Essentially it looks like Yahoo does not want nor will they permit their API to geocode/geotag information that is later mashed or passed-over to Google Earth or Map? Something here IMHO...
"Phoogle Maps (pronounced like Foogle Maps) is a PHP class that integrates itself with the Google Maps API and with the Yahoo Geocoding API to make an easy to use interface to display Google Maps on your site."
Mapperz Note to Users: Check the Yahoo Maps API Terms and Conditions before investing time on this. There maybe infringement using the Yahoo Geocoder with Google Maps.
Mapperz's Phoogle Maps Blog Article