Referrer from checkout options

My client wants to be able to use the referrer field as a sales rep field. However, the way the code works is that it is requested only for new customer registration and/or new customer checkout.  He wants it to be asked at each checkout. I have figured out how to ask each time at checkout in login.asp but not how to update the orders database with the rep (referrer) id and replace the old referrer id in the customer database.

Any suggestions?