Converting multiple incumbent positions to automated Step Increments

We are PeopleSoft HCM Tools 8.59.11 - PUM 45. We are implementing the Automated Step Increment process (we use Position Management) by creating new Salary Plans and Grades with salary steps. The process works great for new positions and hiring new employees into these positions. Our struggle is with the existing employees who share a position and are at different steps of the salary step structure. In one position, we have employees at the very beginning salary of the step structure up through the various salary steps based on when they were hired. When we