You can if you're a contractor or running your own business.
But it would definitely be nice for businesses in general and employment law to stop being obsessed with 40 hours as a magical number. Working 4 8-hour days, or 5 6-hour days, or 4 6-hour days should be just be an option by default.
(And wages have to stop stagnating relative to prices so that the premise of "cheaper stuff" actually happens in the first place.)