It took 2 years, but this finally happened:
Yep. I put Georgia in the stroller like a complete crazy person. We were on a walk, she was hot and didn't want to walk anymore, Oliver refused to sit in it... so I put her in. She even fit with the 5-point harness!
As thrilled as she looks in the photos (I'M THE BABY NOW!), it didn't last long. She wanted out as soon as we started moving again. Which is probably for the best because I got some strange looks from the neighbors.