I am going to be making a sheet cake for a graduation party, and I was planning to put a mortar board on it, using a half 3d ball pan for the bottom, but I can't figure out what to do about the board part.

I considered gingerbread covered in fondant, but I was worried it would be too heavy. If I rolled out gumpaste now, would it be hard enough to stay up by the time I delivered the cake (May 30)?

Does anyone have any other suggestions?

Gumpaste dries pretty fast, I would think a month is plenty of time to dry. Thats what I would do. Or cover a piece of cardboard with gumpaste/fondant. That is what I am going to try. I have a few graduation cakes coming up. I will keep an eye on this post to see if anyone has better options.