Infrequent labor cost addition to service part

We have purchased part 123. We have to add labor to this part when sold as service part. When part is used in production on unit we do not. We can make this a mfg part with a labor cost but again when this part is used in production of a unit in our plant the labor cost is not used. The labor us rolled up at the unit level. How can I sell this part by itself to include labor without having separate part number for this purpose? We currently use E10.0.

Greatly appreciate any help with this.

Thank you