Cut out the two sets of three slat riders on Canvas 1 in the file (black items).  These appear as one big compound vector because the laser is cutting both sides of each joint in one pass.  Add glue and fold around bottom of slat to set for a nice fit. Should be close but not tight.  

On Canvas 1 there's a big circle holder for the Dollar Tree plate used in the photo.  The circle holder should be large enough to comfortably support the plate halfway up the lip of the plate, please adjust for the particular dimensions of whatever plate or tray you want to use.  The goal here is that the wooden frame will hold the plate below the slats so that the top of the lip of the plate is at the level of the slats or slightly above, so that the laser head will not hit the plate while engraving.

While this glue is setting, move on to step 2.

As seen the plate I'm using is roughly 10 ¾ inches in diameter.  The total height from base of plate to top of lip is nearly an inch (approximately 0.95").  If I put this plate on the slats its right at the end of the clearance for the laser (one plate might work, another won't).  So the idea here is that if a piece of wood is cut to the diameter about halfway down the lip, the plate will sit nicely in that circle, and then if that piece of wood is supported below the level of the slats, the plate will sit at a level that allows it to be safely engraved.
 

As implemented with these plates, as shown in the third picture, the top of the rim of the plate ends up just about exactly at the top of the slats, so the laser head is safe but the base of the plate is also within reach of the laser head for a curved surface measurement.

the support arms (labeled A and B) are found on Canvas 2, because Canvas 1 holds all that I could fit into one 12" x 12"  piece of basswood.  If your support piece for your plate is smaller, reorganize to save material.

Each support arm is made from an “A” (on the left)  and a “B" on the right.  The arms have holes spaced at the same spacing as the slats in the P2, so by adjusting the pins that hold the arms together, you can set the size of the support structure.

The holes in the support arms are sized to fit a kitchen bamboo skewer.  However, these skewers aren't finished, so you have to sand it a bit to get a nice fit.  After the arms are cut, use some 120 or 150 grit sandpaper to smooth the skewer and get rid of the ridges.  Continue sanding (hold sandpaper in one hand, run skewer through with other hand, rotate as you go) until the skewer slides without excessive friction through the holes.  Sanding should take 5 minutes, tops.

Then, when the skewer fits cleanly in the holes, tape the skewer into the P2 and use the lines in Canvas 3 to cut pins of equal length.
 

The skewer will curve, and the bowing of the picture from of the P2's wide view camera means that you MUST use repeated close shots to ensure your cut lines are correctly aligned to the skewer.  You may wish to increase the power a little more here to ensure a clean cut.  I used duct tape to hold my skewer because the air exhaust on the P2S blows the skewer around.  Suggest you lessen the air flow and/or use painter's tape along the whole length of the skewer.  when you're done, you get a pile of pins.

If you do it right, the pins insert easily, and can be pushed back out with a pencil.  Use two or three pins for each A/B arm and it will be plenty stiff.

There is no gluing required for the final assembly.  Hang the two slat riders on two slats with the longer side to the inside.  Insert the tabs of the ‘A’ arms to the slat rider on the left, then temporarily support the slat rider on the right and insert the tabs of the ‘B’ ends into that rider.  Remove the support and slide the rider down and it will tighten up.  

Then put your plate support on the arms and etch away.  The design is modular to allow for different sizes of objects, not just plates.  For example you could use this on a tray as large as a cookie sheet.