A couple of thoughts: 1) Incentives for local grocers: Upsell more organic produce. Organic produce is a key component of a successful weight loss diet and they could use branded point-of-purchase materials to encourage more shoppers to choose the higher quality/higher margin items.
2) Bluetooth connection to the scales as an alternative/complement to the rewards card. Once the bluetooth connection to the scale was established, the device ID could match up data from health apps (fitbit, etc) to the "official" weights collected in the stores. This would also become an additional incentive for store participation. Only weigh-ins at an "official" scale would count. Using bluetooth connection between the phone and any of the El Loser Local installed scales also allows multiple store chains to participate without the contestants having to have rewards cars from each grocery chain.