Unless I am missing something, the greatest incentive is for the sub not too lose.
Suggest something along the line of (and this is purely off the top of my head) that each person puts eg $1k in trust of perhaps a neutral party who doesn't need to know the nature of the relationship. If either fails, $1/lb is donated to the players most despised charity IN THEIR NAME. After the set time, eg, 1 year, each "player" gets what is left of the other's money. (I am probably missing something here, but you get the idea - or not! lol)
Suggest interim goals be established, eg, 10 lbs/week.
13 years
