For this you will have to write some scripts for this.
try out the following,
Define a variable of type session (call it this_Session).
In the beginning of your script, add a "Get Contact Info" step.
Set the Session attribute to be variable this_session.
You can now assign any populated strings to the session using the Set
Session Info step.
Place a "Set Session Info" at the desired location (make sure it is
after the desired string variable has been populated).
In the General tab, enter this_Session for the session.
In the Context tab, Add an attribute for the desired Custom Call
Variable, _ccdrVar1 through _ccdrVar5. Assign the desired string.
When you run a report that shows Custom Call Variables, you will see the
string values that were set.