http://www.onerutter.com/open-source/wp-custom-field-geocoder-update-v-02.html
I used a customized version of this with the custom metaboxes library. I had to change the post update action in the geocoder code to ‘save_post’ and give it a priority of 15 so it wouldn’t conflict with the metabox code. I also commented out the response code that displays a geocode error. It must have been timing out sooner than expected; removing it gets me an updated post with the lat/long field(s) populated.