There's a guy on eBay selling aluminum offsets for your Festool Domino; you need a Domino with the original registration pins (round metal pins) as the new square then square plastic then plastic tab registration pins won't work with the system.
I'd post a link to the product, but it changes every time he relists. So, search for "Festool Domino Narrow Stock Spacers".
The idea is simple: cylinders of specific sizes that you can slip over the registration pins (held with a magnet) and use to register against your stock. The spacers put the mortise in the middle of stock from 1.5" wide through 2.5" wide. A side of the cylinder is flattened to allow you to drop the surface registration fence.
When building something with rails and stiles, you tend to have them in a particular dimension and likely there is a spacer for that dimension. You can now slip one on the correct pin (left or right) and drop a mortise right where you want it.
Since I got it, I originally used it on a few stiles; nothing spectacular. The latest hanging cabinet, however, used the spacers exclusively. 56 mortises in record time (besides the Domino's speed). All with no slop.
They seem pricey for what they are, but then they are exclusively for a Festool Domino so the guy knows you have money burning a hole in your pocket. Still, $55 was well worth it. If you can turn aluminum, make your own.