I want to add a check to have atleast one participant in a specific role under Setup participant table

We are useing Windchill 10M020, We have created a workflow where in for a particular task I am asking user to add/remove user from Setup participant table in a task.

But I want to be sure that atleast one user is selected under the define role in setup particpant table before completing the assigned task.

So can anyone suggest me how to check the above condition ?

Regards,

Birendra