I recently embarrassed myself by backing gingerly into a spot, being careful not to back into the other car, only to discover that I had enough room to park another Smart behind me. I remembered this vinyl stick-on wide angle viewer from the days of driving a long van. It works magnificently in a Smart. I don't need to tell you that I'm not a professional photographer, but I hope these photos help.
The cost is $10.00, and most auto parts stores carry them.