I put a ruler next to where I want to make the cut. That seems to stabilize the JT ruler. The JT ruler does help with accuracy.
To clarify, if I'm cutting 3" strips, I would place a ruler on the JT ruler between the 3" and the 3 1/2" slot. It works!!
This sounds like a great idea to add stability--I'll be sure to try it the next time I cut strips with the JT!