does any one know how to make a styrofoam cake that has a cutout to place a real slice of cake in for the couple to cut and feed each other with?

Good question. How would the person know where the real piece of cake is located?

A lot of faux cakes do this. There are tools at the craft store that are a hot knife for cutting styro so that you get a nice clean cut. You cut out a wedge, line it with some sort of acetate or food safe plastic and then insert the cake slice. You do have to mark it some way.