I’m not an engineer, so disregard if this is entirely too difficult or hard to explain, but: how about a device to capture energy from longboard wheels? I’m imagining a belt that attaches to the back two wheels to spin a motor. If it’s snug up against the center line, then it wouldn’t offset the board very much.
You could use balsa wood to make a miniature version, to test it out. It’s…barely solarpunk, in that the energy used to power the longboard comes from calories.