You don't really *need* 40 miles RT. What you need is to ride more or less straight to work, and then take the long way home and ride hard and/or do intervals every-other day.

You could take the long way to work as well, but you would need a shower. My work doesn't have a shower, and besides, if you're huffing and puffing when you get to work it will suck for a good 30-45 minutes.