I've never had to do anything special with my left foot when driving automatics. I put it on the floor and it stays there. I've never felt any impulse to try and press a non-existent clutch pedal. I do sometimes have a problem going the other way, at least at first. I sometimes forget to press the clutch in when coming to a stop, especially after a long drive without changing gear.
Frankly that was the reason I switched to automatics several years ago. I rented one on a visit to the USA and had no 'left-foot problems' but had a few when I returned to the UK and my manual car. I concluded that my body/brain was trying to tell me something so I switched to automatic and have never looked back.