I've had so much fun with this. Had to pull out my PP skills. I think I forgot more than I ever knew. At least the first one I tried was very simple.
As to being 4" square unfinished: try resizing it on a copy machine. The idea of adding strips all around is good. You could cut 1 1/4" strips, that would add 1 1/2" to the total (if my math is correct), making it a 5" finished block.