Hi Again,
After some tests, I realized that even using the trick above you are not able to get more than -60 degrees on tilting kinect. In other words, kinect is able to tilt down -30 degrees itself (according to kinecy_aux stack) and at the same time you are also able to mount the kinect stand with about -30 degrees (more than this figure would not have effect since accelerometer does not allow kinect to go down further even though it can go!) so both of them would give 60 degrees.
My goal was to mount the kinect on the ceiling of my room in such a way that the FOV of kinect would be vertical against the ground. By doing that 60 degrees (30 tilting + 30 mounting angle) with a FOV of (43/2 ~ 22) I could get to -82 and not -90!
Any advice on how to come up with accelerometer is appreciated.