One technique for primary stoker motivation is to find a secondary stoker who is fit, pulchritudinous, nubile and wears corrective lenses. You designate this stoker as "vision impaired". Should your primary stoker be unavailable, indisposed or disinclined, you adopt a selfless air and say, "Don't worry, I'll just ride with my VI stoker, Kaitlin." I'm thinking that the primary stoker might have some ambivalence about the riding with the VI stoker, and be more inclined to participate in the future so as to reduce the necessity of resorting to the VI stoker.
But, I haven't tried this, so maybe someone here can try it, and report how it works out.