How to alias / rewrite path to theme?
URL mappings can be altered with two hooks: hook_url_inbound_alter() and hook_url_outbound_alter().

hook_url_inbound_alter() is used for paths that Drupal is responding to.  See drupal_get_normal_path().

hook_url_outbound_alter() is used for paths constructed by url().

Whether or not you can accomplish this will require some experimentation, as I don't know how the theme registry will complicate matters.