Hello, I work as a delivery driver and frequently forget to turn off my car when getting out which results in my Prius screaming at me so I promptly turn around, reach over the steering column, contort into an awkward position, press my face into the roof, and pretend not to notice how much attention I'm attracting as I claw around for the power button. My question is... How complicated is the power button? In my head it's just a positive meets negative situation and I'm just going to pry off some panels and solder another switch onto the positive and negative wires then whichever one is pressed completes the circuit.
Use the power button to put it in park/shut it off at the same time. That’s how I broke myself of the bad habit of leaving mine on when I first got it.
Won't work, even if you wire the two switches in parallel. There multiple control wires that vary the voltage from to 5VDC. I've actually disassembled one to examine the circuit board. One switch's interference with the other would cause confusion to the computerized circuit.
Glancing in the wiring diagram (more info), it's got two different normally-open contacts, three LEDs, and a key transponder circuit. Ten connections to it. But maybe you don't need to replicate any of that but the contacts. As long as your fob battery works, you won't be needing to hold the fob against the button for the key transponder, and you probably don't care about the LEDs.
The best and easiest option would be to relocate the switch. It would mean getting 22ga multi-colored hookup wire, small diameter heat shrink and a lot of fine soldering. Personally I have quite a few Gen 3 start-stop buttons with some including the snap in plug and pigtail.
If it were my project, I might give it a go with an off-the-shelf DPST pushbutton and see how far I got.
Live a little. The dash has lots of easily replaceable messable bits. You can get buttons that slip right in. If I remember right, open one of those up, it's a pretty common 3 amp DPST button inside.
Pretty sure that mine "screams" the instant that you open the drivers door. Maybe the solution is to SLOW DOWN just a tiny bit.