Does your camera have an exposure meter? If so, set the camera to spot exposure then go to full manual. I'd go about halfway p your aperture (I hear that gives you the sharpest results for most cameras) and move the exposure point around the subject. Adjust your shutter speed (and perhaps ISO) accordingly.
The problem I see, though, is if you have a back light, you're going to have a blown out background regardless. You're camera's probably doing a matrix exposure of some sort, thus trying to get the scene as even as possible.
Have you tried using a flash, or any form of lights in front of the subject?
Here's a photo I took inside an abandoned building a while back. Without the flash, the room was dark due to the exposure/light coming in from the windows. At this angle, I didn't get any glare, thus lighting up the room and still being able to see outside.