Nah - it's easier than that: take two shelves and put them bottom to bottom with their front and back edges aligned. Then use the Domino to make a mortise exactly half way up the stack on the sides of the boards, so that half the mortise is on one board, and half on the other board. The mortise will exactly fit the domino, which will be almost invisible once the shelf is up.

__________________
I don't have as many Festools as Fred. Or Marcou's, or Brese's, or Lie-Nielsen's, or Lee Valley's, or Blue Spruce's, or Harold and Saxon's, or...