Step 1: Get a true edge
Step 2: How much to offset
Step 3: Position in the Workmate
I have positioned and clamped the piece of plywood in the Workmate so a little more than 1 1/2 inch extends above the Workmate surface.
Step 4: Saw
Step 5: Rip a three inch wide strip
You can see the saw's kerf. I wanted the blade to cut just below the line so I have exactly 3 inches remaining on the piece I am ripping. The line is visible and the kerf is positioned correctly so that exactly 3 inches remains.
Step 6: Trim for 3 inch squares
I had my squares fairly quickly and I never had to feel that anything about the process was precarious and dangerous. Using a Workmate this way to make safe and accurate cuts would be ideal where the worksite is away from a table saw and you do not want to risk a precariously balanced saw setup to make a cut.