I knew I’d seen a discussion somewhere before on this - for those curious, I found a post in Guzziriders forum, and a few images. Basically, the example I’ve seen employs a new lever that goes under the right footboard, and the actuating pedal extends forwards and up at the front of the footboard. Not seeing it myself, but for those who fancy the idea:
https://wildguzzi.com/forum/index.php?topic=115830.0
A long while back, I think Harpers were selling a version, but no sign now.