Single signon / CPIC ID issues

We currently have several third party systems integrating to R/3 with XI. Our customer has many restrictions as to who can see what data based on user id. Our problem is that XI is connecting to R/3 with a CPIC id. Since it is connecting with a CPIC id. R/3 is reading that id in order to determine the users profile. How can we have SAP read the users actual id that they used to sign on to the system with?