Your suggested approach might work for you, @lcprop, but it will not work for general application. Suppose you had 20 workers, all being paid and billed out at different rates. The P&L will show the balance of the Wages & salaries account, not a listing of how many hours at whatever rates for multiple employees. That just is not the purpose of a P&L statement.
On the other hand, you could add some custom fields to Billable Time as suggested in this Guide: https://guides.manager.io/9649. Then sort the Billable Time tab listing by employee or project or however you are tracking. Export to a spreadsheet and manipulate.
You seem to be trying to treat your P&L (possibly by tracking code) as the primary input for Billable Time. I suggest you reverse your thinking and consider billable time entries as the inputs. There will be less work overall.