You could copy the values manually using some nested for loops.
3D arrays are so Foranesque. Why not use a class to represent that structure?
I am using a Class (Editor) to encapsulate the data structure and sizing functions. The array is of a custom structure Tile{int Layer,int x,int y, int Width, int Height,int TextureId}
These are to represent tiles in a multi-layer 2d tile based game. Rather than serialize an object I would prefer to keep the structure as simple as possible to reduce file size when saved.