Show customer group money back accuring total.

I give 10% back to customer groups at the end of a purchasing cycle. So, I give customers 3 weeks to buy items such as t-shirts, caps..etc. At the end of the 3 weeks I take the total of their purchases and give them a rebate of 10% of the total of all purchases. Looking for away to show the customer group how much the total is accruing before time is up.

has to work on a multi store.

hope this makes since.

Thanks.