I always thought it would be great to have the ability to search car rental web sites using different AWD#'s for AVIS or CDP numbers for Hertz. See the following threads:

http://www.flyertalk.com/forum/Forum77/HTML/000061.html

http://www.flyertalk.com/forum/Forum79/HTML/000282.html

At present I just check each one manually and it can be pretty time consuming. You could input your list of codes. Don't know if it could handle coupons as well. Sometimes they require usage of specific AWD/CDP codes.