Shelf on kitchen soffit

[Rburt5]

I just finished hanging new kitchen cabinets. The soffit wasn’t level so I had to hang a filler board to give the cabinets a level surface to go up against. My plan was to just cover the filler board with a trim piece. Now my wife said she’d like a small shelf running above the cabinets along the soffit (I know…ugh). Lol. Here’s my question…do you think the shelf will be secure enough for some small decorations if I hang a piece of 9/16 thick trim board upside down along the top of the cabinet and then screw a 1 x 4 onto it from the top as the shelf? Here’s a pic so you can see the filler strip that I want to cover.