"Hotkeys can also be mapped to RetroPad buttons." - How?

Seen here: https://docs.libretro.com/guides/input-and-controls/

There is a tip that says “Hotkeys can also be mapped to RetroPad buttons.” but does not say how to accomplish this.

I want to bind Fast Forward / Rewind to RetroPad R2 / L2 respectively. The only way I’m able to do this is using a controller specific input binding, when I’d like it to be RetroPad wide.