There's a technique in the supplementary manual for the Domino, available at festoolusa.com that puts a piece of pvc pipe on the rod the Domino runs on to shorten the depth to a custom length. You can also put a spacer between your workpiece and the domino.
But I'm not sure that a domino less than 12mm is going to do much for you - thats a very short tenon.
Try it on scrap first to make sure it achieves the result you are looking for.