I want to build a dock for my car

Well, there is a way that should work, but it might be risky unless you have a player to sacrifice for testing! The Fuze and most modern day electronics will shutdown if there is a short on one of the power supply voltages. The Fuze DIY lineout cable uses pin22 as a 3volt feed to pin7 to enable the lineout function (Hey, that’s my claim to fame here!). You could wire a tiny momentary pushbutton switch from pin7 or 22, through the switch and then to ground. Pushing the switch will ground out pin22 which will short the 3volt supply to ground. This should cause an instant shutdown of the player due to current sensing shutdown. I would not attempt this without testing as it could be death for the Fuze if wired wrong.