[Plugin: Basic Google Maps Placemarks] Add a custom metabox to placemarks?

I would like to add a custom metabox (or at least some custom fields) to the placemarks post type to handle a client’s specific needs. I usually use wpalchemy for metaboxes. I’m doing my normal wpalchemy thing to add a metabox, and it isn’t showing up. Is there any way to do this without editing the plugin?

Thanks!

http://wordpress.org/extend/plugins/basic-google-maps-placemarks/