Async Loading Screen

Can anyone give a clear explanation on HOW to call StopMovie() “in the slate thread”. I have created a function inside the SLoadingScreenLayout that has the call to stop the loading screen. Now I have to figure out how to trigger it! Most of us operate in the Game thread. There is documentation on how to access the render thread, by enqueue, but not much on the slate thread. Do I set up a tick like loop in SLoadingScreenLayout waiting on a sign from the game thread? How do you safely cross the threads?