I think the best option would be to hook up a momentary relay to the acc power switch on the ignition and run that to a docking station power switch.
Alternatively some people open up the laptop and wire the power switch to the 2 pins on the modem socket (disconnecting the modem of course) and them using a 2 wire modem cable that can be hooked up to the previously mentioned relay set up
Then you can set the power button to enter standby when it is pressed from within the power settings of windows etc.
As far as laptops go though, unfortunately there's not much option but to do some soldering to get a remote power on solution.
I've also looked into Wake-on-lan options but I havent found anything other than another PC that can send magic packets to wake your car PC so its kind of pointless.