I've not tried this personally, and am now curious to see what others have to say about it.
My gut tells me that the combination of the backlight from the LED light table and the frontlight from the scanner are going to cause you headaches.
My current solution has been to scan my 4x5s as two strips of medium format film, and stitch them together in post. But my current "card stock and tape" film carrier leaves more than a bit to be desired. [In part because I can't find it, and also I never came up with a good solution for reliable registration of it that was cheaper than upgrading to a better flatbed scanner that supported 4x5]