Yes, agree with the others. For Tilly, she was started very young out in the field with the training dummies. In gundog work, the word 'stay' is redundant.
Because you tell the dog 'sit' and sit means stay sitting until i tell you to do something else. So, we got tilly to a good place where her retrieval drive for the dummies was good and strong, raring to go but out of maybe 10 thrown dummies, she would only be allowed to pick 2.
The rest i would retrieve myself and her job was to hold steady.
Whilst she had that work going on in the field, at home in my kitchen i would practise this by getting her to stay still whilst i rolled balls past. Slowly at first and far away, then closer and faster.
As i wanted her to hold steady but still maintain that drive to go when needed.
As the months went on, we started to get into other things and not do as much gundog stuff though we still do bits and bobs now and again.
In your situation, you probably do want your dog to switch off and not be driven to go after the thrown objects.
So, once you have trained a solid down stay (usually more stable than sit stay) you can start slowly by walking round your dog, return and praise in a way that does not cause whisp to bounce up. A small touch, a gentle 'good'
Then walk round again.
You can build to waving your arms, jumping, anything you like.
With the rolling balls, start very slowly and roll further away. You can use a hand signal to reinforce the stay.
Then it is practice, practice and more practice!
If you are having no luck at all, get someone to help you by holding whisp on a short lead.
At the basis of this is a really good stay. Then stay with distractions.
(I do a lot of cafe trips with tilly where she is expected to settle for up to 2 hrs at a time without disturbing anyone. There, i do expect her to switch off. She is very well practised at that, and it is very very handy)