Here’s a fun little tutorial from everyone’s favorite Aussie Lama, Shane Miller. He explains how to create and install a “sprint shifter” using a Makey Makey (and, of course, a cutout photo of Cavendish’s face).
A true sprint shifter (for anyone not familiar with the term) is a push-button shifter mounted within reach of your thumb while in the drops, making it easy to shift while sprinting.
Shane doesn’t actually create a sprint shifter here, but instead makes a shortcut button which activates a Zwift powerup (such as the aero helmet) at the push of a button on your handlebars. He does this by wiring the Makey Makey button to emulate pushing the space bar on the keyboard (which is how you activate a power up in Zwift).