Clarification required for using API

 
Created a paygroup and wanted assign 10,000 salesreps to paygroup through API.

I tried taking cn_srp_paygroup_pub.Create_Mass_Asgn_Srp_Pay API .But there is a  input paratmeter role_paygroup_id .And this is attained only after attaching role to paygroup which eventually assign all the salesreps which takes longer time .

So,how to attach the Role and 10,000 retailers to the paygroup is there any other standard API .

Please advice !!