Conditioning input signal range for sensor
The piezo element is capacitive in nature having a very high DC resistance. The effect of R1 and R2 are therefore insignificant. Use two potential dividers connected to either side of the piezo element and that should work.

Use high value resistors (> 1M ohm) so that the signal is not affected. However, you might find that high value resistors create an offset problem with the monitoring circuit you are using; bias currents from the circuit pins may not be equal and you end up with a small DC offset. This may be acceptable but, as I don't know the application (or the device) I can't tell.