In short, no. I tend to run out of steam after about four or five hours, having to stay an extra three or four hours after the eight would just be a waste of time, piss me off and not get anything accomplished. Additionally, he's basically asking you to increase your work time by at least 25% for free. Nice try there, buddy.
Assuming your boss is a reasonable human being (a little difficult to believe considering he even suggested this), you should be able to convince him that this is a horrible idea. Otherwise, start polishing your resume, it's time to jump ship.