How about introducing Mega Rewards! It would work something like this…
On a totally random basis (lucky winners from every few hundred/thousand/10’s thousand or even a fixed number of users per month) would receive an instant Mega Cashback Reward on a purchase. This could be 5%, 25%, 50% etc of the card purchase up to a max of £x
It could be set so the higher the tier the more chance you have of winning.
It could be a good incentive for Curve customers to spend more often on their cards.