The spurious payroll is the solution, remembering the context is an LLC with members who aren't/can't be paid salaries, setting up each member as an employee with the appropriate rate that they are paid, and all the typical withholding etc. of  the typical salaried employee set to zero.

The item that is billed for the member's effort is set to the rate charged to the customer. 

The COGS then reflects the cost of the member's time correctly, while the excess income over that is not.