Multiple Job Roles for Competencies

I need to be able to include all competencies of an employee that performs multiple job roles. Currently an employee can only have ONE job role.

For example, we have operators that perform the following job roles dependent upon necessity: Tank Car Operator, Tank Truck Operator, Railcar Operator, etc.

Each of these job roles includes their own competencies. Every operator is assessed on each of these separately. Therefore, the need to be able to have more than one job role assignment.