A client wants items packaged in a certain way, and there would be a charge for this.

This assembly or labor feature would not necessarily be available publicly. Also, there may be other clients who want assembly or labor, but different setups or output. The labor scale might vary client to client.

Thus, I'm wondering if there might be a way to add some custom fees for a particular client, and on a sliding scale (depending on order value).

I don't think this is possible, but if anyone has any thoughts, most appreciated