Two things: I'm surprised nobody mentioned this. Buy a recumbent bike and try maxing out on bench press as you ride to work. It's unconventional and difficult, but when properly executed...a thing of beauty. After a month or so of that, a 3 miler won't seem so bad. Another thing you might want to do is see if you can find a route to work that is downhill in both directions. Many will tell you that this is impossible because of physics. I say they're only limited by their drive to find an easier way to do something. Hope this helps.

Most of the changes are mental. Once you get your routine down it will get easier. Eventually it will become second nature.