App note from Kionix on reading multiple accelerometer by a single ADC using off the shelf chip or accelerometer built-in multiplexer. Link here (PDF)
A Kionix tri-axis accelerometer with analog outputs provides three output voltages (Xout,Yout, Zout) which are proportional to the respective accelerations in those directions. However, with three analog outputs to digitize, it is possible that the system microprocessor does not have the necessary A-D converters. One solution is to use the internal multiplexing capability of several Kionix accelerometer products to multiplex the three outputs to one analog signal. Another solution is to use an off the shelf multiplexer to multiplex the three outputs of the tri-axis accelerometer to one analog signal.