Dog, I bought the same table a few of years ago. When I saw the extras on the other model I rang Wolfcraft about getting the box joint accessory & was told they are illegal because of safety fears. Not to be put off, I made my own. The first pass snatched the wood throwing it accross the shop. I could so easily have had my hand pulled into the cutter by the force.
Never again. I've been using machinery for 40 years and that was the first time I've got close to a major injury.
A far better , and safer, method is to make a jig to hold the work that rides in the mitre slot.
I made mine by screwing a length of 18mm ply to the mitre gauge then ran it over a 3/8" cutter. Move the plywood exactly 3/4" towards the cutter then make another cut. This will be exactly 3/8" from the first. A short length of 3/8" hardwood fitted in the 1st slot completes the jig. I added 2 square sections of ply either side of the mitre gauge to keep it at 90° to the table.
Now you can clamp the workpiece to the ply making it 10 times safer.