I just bought a new battery powered weed whacker that has
the idiotic and wasteful auto-feed feature.
After an hour or two of thinking about how to disable / bypass it -
a lightbulb came on and I did a youtube search -
- first hit ! :

https://www.youtube.com/watch?v=_7I2uX8ziZ4

I haven't tried it yet but will-do later today.
The idiotic reply to this problem, from Ryobi, was to
1. don't start-stop so much when using
2. buy our other model that costs 2 X the price
Gee thanks Ryobi ...
John T.