Seems like a poorly thought out way to motivate somebody. In addition to the obvious advice of "find a new job immediately", if it were me I'd be sure to demonstrate to the boss in question that it doesn't work the way he thinks it does.

Pull out a calculator. Assume you were previously working 40 hour weeks (he loses those 3 overtime hours a day as a matter of course). Now multiply by your new salary and divide by the old one. That's how many hours per week you're going to work for the short amount of time you're still there.

If your boss notices and complains, you can explain the math to him, and calculate the figure he'll need to pay to get back to those 55 hour weeks he was previously accustomed to.