As an ex-pillion here's my tuppence...
I used to ride with my left hand holding the rider (generally as much of his jacket that I could bunch up.
), right hand holding the grab rail. Always had knees ready to squeeze and heels/toes ready to dig in.
e.g.
Braking:- grip rider with knees and dig heels into footpegs to take some of the strain of heavy braking from right arm (I'm right handed). Obviously adjust according to amount of braking. Don't forget stomach muscles to keep upperbody in place.
Accellerating:- left hand holding rider, right arm pushing against grab rail, toes dipping down on footpegs. Knees, well... gripping the rider... lots.
On the motorway there wasn't much reason to ride like this so I'd just hold the rider with both hands and grip knees.
Was told about that sticky matting stuff for the seat... looked pretty efficient. But then I got my own bike.
