I'd add a 3D digital accelerometer to deduce the direction of the gravity vector and if not orthogonal as expected, scale (no pun intended) the measurement per the gravity skew.

Now, for use off the surface of planet earth, or use in motion, this becomes very necessary.

Hmmm, would an intelligent accelerometer riding on the scale be able to deduce unloaded conditions to re-zero and autocalibrate? Not without envelop interpretation.

Here's my business card:

[duh inc.]