I cannot coach without small sponges.
The sponge is the best coach.
Normally I ask nicely that gymnasts keep their feet together. If they cannot, I hand them a sponge to hold either between the feet or knees. If the next attempt is successful, they no longer are required to use the sponge.
I have coached kids who have never been asked to use a form foam. And kids who need the sponge almost every attempt.