Code to work with Aweber

Aweber has the ability for me to ask my customers what month their birthday is in, and I can then send a message to them in the month of their birthday. However, it does not have the ability for me to deduct a couple of weeks from their birthday so I can send them a message with a coupon a little bit before. I am looking for someone who knows aweber well enough to make this happen for me. Thanks!