Ran into this problem while I was play-testing a lot I was about to put up in the Gallery and one of the sims visiting the lot made grilled cheese sandwiches. When I went into build mode, the plate was still there so I worried how this would affect the download.
The solution above still works! I dragged the plate in an empty area outside my house, made a tiny room around it, then sledgehammered it away. I think it actually got deleted as soon as I put a wall on top of it but still had to make sure!