This kind of rings a distant bell. I recall, way back when, somebody made a temporary passenger side mirror that the mounting arm tucked into the window glass channel and all you did was roll up the window which trapped the mirror mount where ever you wanted it. It was for people carrying a load to help to see the right side when your side visibility was impaired. This was back in the days when most cars only had one outside mirror. I might have seen it on JC Whitney or a common auto parts store. Good luck! Another thought is once you have your car in the position you are happy with in the garage, put some high visibility tape on the floor right along side your driver side tires, front and back. You could then just crack the door open slightly and aim for the tape while backing up! I know someone who already does that, ME! And I already have dual mirrors! I do however have an excuse, (I'm Old!)
