Leave the the shifter in gear, like put in R or keep in in D, turn off then shift it to P. As long as you turn off while it's in R or D the radio will stay on, or the phone, bluetooth etc....
If you leave it in R, you still able to see the back up camera, a great way to keep an eye out for kids or such.

I think you can keep it the power on for 60 min (or maybe less).

 

 

Once you push the button to turn the car off, why don't you just push the start button again without your foot on the brake? This should turn on only the accessory power and not restart the engine.

 

Yes, but you need to press the button twice WITHOUT your foot on the brake if you want to open/close the windows and sunroof.