An undistorted whole body shot in a 10x12 room? Why is that necessary? Is there something special about that room and is there a client who demands a full body portrait in that "special" room?
First, you don't want to use a lens smaller than about 28 or 35mm on FX or 18mm to 22mm on DX or you will start to distort the image. So lens choice creates some distance limitations.
Second, make the subject smaller by posing them sitting in a chair.
Third, use your legs to find another location. The room is too small. Admit it instead of trying to fight it.
Fourth, every room has a door. Back out the door as far as you can and shoot through the door to gain as much additional room as you can without letting the door frame into the photo. You probably can extend a room 3 feet this way. If you are using on camera flash bounced off the ceiling this could be a problem because the bounce flash may be trapped by the casing above the door so shoot available light. At the very least you can get your body outside the room with the camera in the doorway so any bounce flash stays in the room.
Fifth, it might be possible gain a few feet of distance by shooting through an open window but this is going to involve "set up" because you are very likely to need a ladder on the outside of the house.
Sixth, change the way you hold your camera. Place your camera on top of your head, kneel and lean your back up against the wall, trip the shutter. By taking your own body away from the back of the camera you have effectively enlarged the room about one and a half to two feet. Sure your framing will be hit or miss. Take lots of shots and see if you can happen to get one you like. If you have the ability to shoot tethered run your live view LCD output to a laptop screen which you can watch while the camera back is placed directly against the wall. Now you can see your framing as you shoot.
