As such SAP standard does not have the capability to add the rates of the wage type in standard.
there are couple of option to solve this problem
1. Create another wage type and add the rates of the required wage type to display it only payslip.
This would mean that you have create a dummy wage type in 15 or 14.
2. Create a technical wage type that is not specific to any info type.
the all is the best option,, convince the customer to retain as 2 line items in the payslip , as it was the customer requirement to create 2 different wage type.
Thanks