On a serious note;
Practice them on a downwards slope. That way you can just start again without pedalling up to speed when you drop the back wheel every two seconds. You’ll get much more actual front wheel time and braking practice than if you’re taking a run up for every attempt.
The same slope will also be perfect for coaster wheelies which will become awesome manuals.
Ahh, memories of spending hours learning to manual and stoppie in a dry and covered subway tunnel.
I could hold a manual or a stoppie indefinitely when I was 16 but it’s been about that long again since I tried.