TOPIC: Multiple Promo Codes - One Discount

Hi,
I am trying to figure out a way to solve this issue. We advertise all over. We want to know the source of discount code. When someone registers, we want them to get the discount. We want them to put in the discount code they got from (For example Yelp) so when we look at it, we can see if we should keep advertising with them. I know i could create one discount code for each advertiser, but that looks messy and cluttered. Is there any way to do this?
Thanks
jon

There is no way to detect where they acquired the discount code without using different codes.