When booting an instance there is a typical ability to set metadata on that instance, which when booted the instance will have access to. This is used by various folks to pass in information into the instance (this info really isn't userdata but is used by at least godaddy for things like login_user for ldap and such...).

$ nova help boot | grep -B1 -A2 meta_data.json
  --meta <key=value>            Record arbitrary key/value metadata to
                                /meta_data.json on the metadata server. Can be
                                specified multiple times.

It'd be really nice to have a way to provide those values (or setup the defaults for those) when using the plugin, likely in a way that allows for specifying the keys and values multiple times (a dynamic list form that u can add as many as you want would be awesome).