Or get a big widescreen!
GTR supports it, and you can see much further across the car, I don't know if you'll be able to see the mirror though, you may still need to edit that file, but not by as much. I run at 1920x1200 on a 24 inch Dell monitor.
Your eyes generally dont see a square view like on a monitor, widescreen is always closer to what you really see.
Matrox also do an external breakout box that will make 3 monitors seem like 1 monitor. So if you got 3 x 19 inch lcds and the matrox box you could run gtr at
3840 x 1024 which is probably good enough to see the mirrors.
Im assuming money is no object of course