I have a similar issue for deployment mode. Basically I want my GWT to be managed from a single entry point deployment and be able to run it as widget on 3'rd party websites, without them have to download my application into their host, only using the selector script as reference to my GWT app.
There is a problem doing that due to SOP limitation of current bootstrap process that uses an "iframe" to load the compiled script asynchronously.
I created a workaround procedure for that, let GWT app be installed using 'script' instead of 'iframe'. This makes my GWT available for 3'rd party websites, and let me maintain a single entry point of deployment.
The following article describe my workaround procedure:
Make GWT Widget Avialble For 3'rd party websites