In some cities they reward you for returning bikes to certain locations that have a borrow/return ratio imbalance. For example, they will add bonus minutes to your card so if you go over the standard single-trip time period (e.g. 30 minutes) you can use the extra minutes to avoid getting an extra charge.

They should offer a cash reward that is less than their internal cost for a rebalancing operation. They should also implement congestion pricing. In Manhattan, I would love to be able to ride a citibike crosstown in mid town. Both stations are full in the middle of the day. If I take a bike out of the dock on the east side, I should get a credit, and I should pay money when I dock it at a busy station on the west side. It would be a wash for me, or I might pay a little. The upside is, those trips should be very easy for citibike to fullfill, it's not like riding out from an empty bike area to a crowded area.