You could mount a resistor on the lever arm, in view of the PIR sensor, and provide enough current to it to raise its surface temperature above ambient by a few degrees... amount necessary depends on sensitivity of the PIR.
You may possibly not understand how a PIR sensor works. Typically there are two pyroelectric sensing elements connected in series opposing.
Here is a link to a website that has a basic explanation.
Each sensor element produces an electrical output only when its temperature is changing. That means they cancel each other out when their common ambient temperature rises or falls. However, the field-of-view (FOV) of each sensor element is slightly different, by virtue of the two elements being physically separated and a plastic Fresnel lens focusing two slightly different (displaced) images on the sensors. When motion occurs in the FOV, one sensor will produce an output signal that is the opposite polarity to the other sensor. Since they are connected in series opposing, this differential signal represents motion across the FOV. In actuality there are many Fresnel lenses, arranged to cover a volume of space with overlapping FOVs, for any practical PIR. You can cover individual lenses with aluminum foil to limit the motion detection area and therefore prevent false-positive motion detection.
