It really is a battery killer to be in an area with bad 3G coverage. I always had to do this on my previous phones. I think there's a way to do it in a hidden menu here, but it's a PITA.
What solved it for me on Android is that I leave wifi connected when I'm both at home and at work. Set wifi sleep policy to never too. Phone turns off mobile network and keeps the wifi connection constantly. WAY better on the battery.
Can you get in wifi at your office?
Good luck to you finding a solution.