Avoiding switching transient in IC switch
I don't see how a serious transient that would affect a relatively slow op-amp is being caused directly by that switch, nor do I see any problem the way you're using it in general. 

Do you have a resistor directly across the piezo (not from the non inverting input to ground)? If not, then leakage may be causing the voltage to rise across the piezo while it is disconnected, and when the switch closes you get a transient as the piezo capacitance discharges.