An alternative to thumb brake, Danny Sailer aka Ripperton Electric bike bloke had fitted a throttle brake on the left clip on his old CBR1000RR. He said It worked for him. Remember either Doohan on Gardener used a thumb lever back in the day when the 500GP oil burners tried to throw their riders overboard prior to traction control and electronics goodies. Troy Bayliss did OK without using rear brake winning one MotoGP race plus a couple of Superbike titles.