Beyond the Target Stick

Q: I have started target stick training with my 4-year-old lab, Carter. He is very quick to learn and really enjoys it. I've gotten him to touch the stick in many situations, and have shortened the stick, but he still wants to touch the end of the stick when I say "target." Where do I go from here? How do I teach him to touch objects and not the stick each time? I would like to teach him to maybe turn lights on and off or something challenging and interesting. He learns so quickly he needs a constant challenge. Any suggestions?