Ok, I figured out how to make the Amazon-Mercedes deal profitable with bike couriers:

The Mercedes Benz Sprinter vans they're selling for $10k have a retail MSRP of $34,000. So what you do is plan out your logistic in terms of how many vans you will need with or without the bike couriers. Then if you can get away with using one van instead of three because you're using, say, five bike couriers; then you take the amount of the subsidy discount (i.e. $23,000) and you pay that subsidy based on how many packages are delivered and not how many vans are sold. That way, the companies are investing in subsidizing deliveries and not van sales. So $23,000X2=$46,000 to split between five cyclists, which comes out to a little under $10,000 each. Remember that the driver is already getting a $23,000 discount on the van.