Proxy ADSL users

Dear All, is there any way to limit the access for ADSL user to be from a specific ATM port? I have an ATM DSLM and want to proxy the request to a specific ISP, depending on some attribute, and need a help to do know the attributes which i can use to do that? i did that for the dial up users using Called-Station-Id, but for the ATM DSLM i didnt know what can i use to do the same?