It's possible that if you were to do your checkride with either a FAA inspector, or a company check airman with designated examining status, the person doing the checkride might agree to fulfill both actions during the check. That would be unusual, however.
Most companies won't consider you for a position unless first you have the basic qualification for the job, which would include being appropriately rated in the aircraft.
An exception to that is obtaining a type rating and the ATP; in some cases you will be able to take the ATP ride at the same time as the type ride, because a type ride is done to ATP standards and they can easily cover the same ground.
In order to obtain a single engine land rating on your commercial during a 135 checkride, the person providing the checkride would need examining status granted by the FAA, or be an FAA inspector.