Tested my 'flasher button' activated version on the weekend.
I should have done this 12 months ago - perfect!
As I left the bitumen and hit the dirt at around 70km/h, I simply flicked the button (no taking hands off bars - or worse stopping), and the ABS light illuminates.
Later on restart its reset (how I want it). If I ever do forget to cancel when off road it's only going to take 1/2 second to cancel again.