That's similar to what I've been playing with,

My domino "skin" is 6mm MDF and I use a 6mm spoiler skin below/adjacent to it, under the workpiece... both being the same thickness, all I have to do is build up under the domino "skin" with the same thickness as the workpiece.  Using the TSO loc-dogs I have an unobtrusive clamping system.
In the above picture I have pieces of 12mm MDF to lift up the dominos and under the shaper there is a 12mm workpiece with the 6mm spoiler underneath... that way I'll only have to replace 6mm thick MDF marred by the through cuts... closely considering 3mm "skins" as I only plunge through 0.5 to 1.00mm.

Still learning, but though introduction of the Shaper product(s) to Shaper newbies is opportunity lost if I waited to review once I mastered it, down the track.  

If your first cut is too short... Take the second cut from the longer end... LBD