Issue in Match Transform in SAP BODS 4.1

Hi Experts,

I am using SAP BODS 4.1.

The issue is with Match  Transform .

I have Customer id ,Name and Address field .And I want to use name address match  Transform to group the customers on the basis of Postal Code and Name of Customer.

But while doing that ,I also want  to nominate the customer with lower cust id as the Driver Record(Master Record) and the others with higher cust id as the passenger Record(Duplicate Record).

I understand that we have to use Group Priority options  and have to pass cust id  for setting the priority ascending.But when I am trying to selct the input filed in priority,it is only allowing me on the basis of output fileds , like Person Given nname,Break key  etc.

Can you suggest me how to prioritize on the basis of Cust id ???

Thanks ,

Mayank Mehta