Give him three options:
More pay
Ownership stake
Look for your replacement
That's the boring answer. "You want more ok gimme more". The real question is, do more hours result in more work done. From personal experience, no.
No, your boss should be asking if more work is getting done. Getting work done is only a secondary goal as an employee, for your boss it is the primary goal. Getting compensated for the hours put in is an employees primary goal. It's nice to get work done, but I can think of better ways to spend my time than working...
The GPs options (direct pay, ownership/indirect pay, or else...) make more sense as an employee. If getting work done is a primary goal to you, and you think you won't get more work done by working longer hours, you can always tell your boss to go fu^H^H^H^H^H reconsider his request.