Let me say at the outset that you are responsible for insuring that this design is safe for whatever use you wish to put it to. Used improperly this can cause injury. Be safe and sane, people.
Step 1: buy Amazon items B001E95R1S and B01N99XMM2. You will also want to buy 7 round-head #8 5/8" wood screws and #8 flat washers. You will need a drill with a 1/8" bit and a power screwdriver for the wood screws.
Step 2: Unroll the chair mat and lay it flat. Weight it down and leave it for a few days so that it loses its rolled up shape memory.
Step 3. Measure the top of the stool seat and cut a rectangle out of the mat about 1/2" smaller in each dimension. Try to arrange the rectangle to maximize the number of "pegs" that remain inside of it. Cut that rectangle out of the larger mat. You can do this multiple times, perhaps getting 8 or 9 stool-sized mats out of one larger mat. Use some 60 grit sandpaper to smooth the cut edges.
Step 3.5 (optional): Use some 120 grit sandpaper to ease the points on the studs if you want to moderate the severity.
Step 4: Center the mat with the stud side up on the top of the stool seat. Using the 1/8" drill, drill a pilot hole through both the mat and the seat in the very center of both. Place a washer over one of the wood screws and drive it through until it's home.
Step 5: Check that the mat is aligned and centered properly. Perform the drill and screw operation to make a figure H (so one screw in each corner, one in the center of each long side and one last one in the overall center).
Step 6: Assemble the stool as its instructions indicate.
And there you have it. The threat of just one minute on the punishment stool will put a stop to any undesirable behavior your sub/little/slave/whatever may be exhibiting. Of course, making them sit on the stool nude with their hands behind their head is highly recommended. Maximal impact would be achieved by also requiring them to not support their feet on anything.
