It might be easier to just hook up a few solar cells to the hamster wheel. When you open the frunk, light would hit the solar cells and the wheel would start turning.
This should work:
Amazon.com : ALLPOWERS 2.5W 5V/500mAh Mini Encapsulated Solar Cell Epoxy Solar Panel DIY Battery Charger Kit for Battery Power 130x150mm (Solar Panel Only) : Patio, Lawn & Garden
Assuming the panels have enough power to get the wheel spinning at a decent speed, that's actually a great solution from a bunch of perspectives, with opportunities for teaching moments along with the original joke. I like it.
Edit: Just realized that the batteries and switch are in the hamster - and the wheel is braced on both sides and contiguous on the bottom. That means this particular hamster and wheel isn't compatible with a photocell switch or solar panel unless you put them on the hamster itself, which wouldn't work out too well I think.
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