I would either find another job or maybe talk to your Human Resources people about this. Not sure if I understood you correctly but there could be some labor law violations and/or some violations of your contract or work-related agreement (If you have something like that in place to begin with). And, sounds like your boss is operating this position without any kind of a backup plan too. i.e.: someone calls in sick or quits, no one available to relieve.
Personally, I would tell him to kiss my butt (In a very tactful way) and I'd find greener pastures somewhere else.
Charlie
"Good and evil are present in this world, and between the two there can be no compromise" - President George W. Bush, in his farewell address to the nation.