How to specify a threshold on the project bill rate

Summary

We want to set up a threshold on the bill rate for employees whose time is getting billed to customer

Content

We have a scenario where in employees bill rates are multiplied with a labor multiplier and gets billed to the customers.

But we also have a threshold on the bill rate not to exceed certain amount.

Eg: Employee ABC has bill rate of $100.  Labor Multiplier is '3'.  When invoice generation is run, the bill rate gets calculated as $300 multiplied by no of hours.  But in some contracts have clauses that the bill rate should not exceed $250.

One option is to define a override schedule for the employee.  But this process is manual and time consuming and not automatic.  Users first review the draft invoice, identify these cases, modify the contract to define overrides and re run the draft invoice.