Try this. Use a large pliers to squeeze the spring together. Get a plastic Zip tie, or equivalent and form a small loop in it. Squeeze the looped end into the gap that forms at the ball-end of the spring (inside the bracket). Gently remove tension from pliers, allowing the plastic to be wedged between spring and bracket. Carefully position the mirror mount back into its opening allowing the trailing end of the plastic tie to hang down into your coupes cabin. Once the mirror mount is in position gently tug the exposed tie-end. This will cause the other plastic end to pop out and allows the balls to engage which should result in securing the mirror in place. If successful, have cold beer and watch some old episodes of Thunderbirds with your two year old...