UMG: How to dissable marching ants for a better preview

In the lastest 4.8 build there’s an option to show a background mockup picture.
That’s very cool but with all the “crap” on the UI (marching ants area selection: ) we still have to go play the game to see what the UI really look like.

Is there way to get rid of it like the “G” key for the 3D viewport area?

If not, could you suggest this comment to person in charge of this?