No worries.
In actuality, I have wondered about the possibility of being in a situation like this myself....but from the old gentleman's side, since I routinely carry a cane (larger diameter and bulkier than normal...and could be mistaken for a shotgun in an adrenalin-fueled situation).
It has been many years since I was last pulled over, but if it happens in the future, my plan is much like what JumboFrank stated.....windows down, engine off, hands on the wheel until directed to act.
If asked to exit the vehicle, I plan to clearly and verbally communicate the unique method it takes for me to exit my truck (because of the way I have to move my prosthetic left leg), along with the mentioning of my cane.
** I was pulled over once for no particular reason (profiled for being in the wrong place at the right time I guess.....but that is another story ??) before I had a prosthetic leg. When the officer asked me to step out of the vehicle I said, "Sure. Be glad to if you'll be so kind as to hand me my walker out of the back of the truck...or let my wife get it."
The officer kindly let me sit in the truck with the door open (while waiting for the drug-sniffing K-9 unit to arrive...remind me to tell that story some other time).