The answer is yes, you can attach the SawHelper to a Kapex. E-mail Mr. Brice Burrell of Burrell Custom Cabinetry in Pittsburg, PA. He is a regular contributor to various sites having to do with Festool. You may need to call his shop as his e-mail address is not obviously apparent on his website at http://www.burrellcustomcarpentry.com/about.html .
The short story is that he has done away with the z-shaped brackets and the portion of the wing that has the screw-on knob in favor of directly attaching the wings to a pair of the Kapex side extensions. Fastening the wings is as easy as atttaching the side extensions on per normal procedure.
Mr. Burrell is one smart craftsperson. His website is filled with pointers on Festool, SawHelper and a few other timely tidbits. Give it a try, it is well-worth your time.