Hello, currently we can extend these, perhaps you could offer long term users the ability to extend these for longer durations, month-6 months- year. With each increasing length of time offering a discount on the cost of donut cost.
ie month saving of 10%, 6 months saving of 20% and a year extension offering 30% discount on the initial cost of purchasing booster.
It would likely increase the number of persons buying larger donut packages, and mean they are more likely to continue playing. Anyway it is just an idea.