Friction drive e-bike conversions were popular years ago. They generally: * Wear tires surprisingly quickly * Absolutely suck in any form of weather or terrain condition (dirt, rain, etc.) * Have ~20% less efficiency than any other drive form. But, they are easy, and they do work.
A Skarper system [0] that drives through an adapted brake rotor sounds [1] like it is the way to go if really want [2] a well thought close to non-permanent conversion solution.
[1] https://road.cc/ebiketips/review_v2/skarper-ebike-drive-syst... .
[2] Compared to other conversion options they are currently expensive https://road.cc/ebiketips/content/advice/buyers-guide/best-e...