Yep, I agree with CoriAmD.
Tumbling blocks is the way to go. And it depends on how detailed you want to get, but I would imagine each side of the block would be broken down into 9 sections.
You don't have to have the blocks touching, but you could make various permutations of the colors on the cube (solved and unsolved) set against a solid background background.
And Y-seams are not be dreaded. ;-)
I'm sure your son will get a big kick out of it.
Here's a really sloppy quick rendition of a possible block (from EQ), just to give you an idea.
Even if you just do one BIG block in the center, there is no mistaking what it is, especially to him. I noticed there are now 4x4 and 5x5 cubes...you can make some that size.