It sounds like a SMOP (simple matter of programming), except for the part of no power. Note, in the software business, SMOP can often times mean that how to do it obvious, but getting all of the details right is hard.
You need power to handle the PIR sensor, so you have to accept that you will need to power it, which means batteries and/or being powered by the mains circuit.
Essentially what you want is an AND circuit, where the condition is true only if the switch is pressed, and there hasn't been motion detected by the PIR in the last quantum of time. You could implement the AND logic in the microprocessor, or use a relay that the switch feeds through. Obviously every time you detect motion you record the current time plus the time of to reset the logic, and you don't allow the switch to complete the circuit if the time is within the motion. If you haven't detected motion in the timeout period, reset your condition variable or change the relay to allow the switch to function normal.