Add an industrial electric bin vibrator on the under side of the chair to add a little extra tingle! An alternative is a large hand-held body
massager for chair. Screw the vibrator to the chair bottom with hidden metal straps or bands, and use your PLC to turn on the 120 volt vibrator power when your seat switch is triggered.
Your chair is wooden like all the old electric chairs, right? If you strapped a 120 volt vibrator to a metal chair, a short circuit could cause it to become a real electric chair.