Here's an example, the grand finale of our little game. Shyla stood on cardboard and stayed on it as it slid on our driveway.
Here's a video of the steps that I used to get Shyla to this point. It was much easier than I expected! I'm glad that it was easy because it was very tough on my back!
Notice that I started with her mat, which she knows. I let her lie down the first time that I slid her on her mat. Then, I transitioned her to standing as she slid. The third step was switching from the mat to a big piece of cardboard, and having her slide on the cardboard across a smooth floor. The final step was taking her outside to our rough driveway and having her slide on the cardboard. Notice that I started with very short bouts of sliding. Then, I increased it a little bit at a time.