You cant adapt it, but which Pioneer do you have? A lot of the nicer Pioneers have what they call ASL (automatic sound level). It senses the increase in voltage from the alternator and will increase the volume that way. See if you have it and turn it on (its default is off). I am pretty sure the plastic shaft you speak of, is a support to hold the rear of the radio, to keep it mounted solid in the dash.
__________________ -There are 10 kinds of people. Those who understand binary, and those who do not.
-If we ever forget that we are One Nation Under God, then we will be a nation gone under...Ronald Reagan