Elon said the idle fee only applies on busy stations. I've taken close to 50k miles on road trips on Superchargers and visited almost 60 different Supercharger locations. In the vast majority of cases I was the only person there or maybe one other car. Very few times was a station more than 50% occupied. So in all these cases, having the car plugged in longer would have been totally fine and you would not have been charged an idle fee.
When you know you are going to stay longer and the station is very busy, how about only charging as much as you need and plan your long meal at the next station. I just drove from Los Angels to Wisconsin. 16 Supercharger stops. At none of the places would there have been any problem with staying 20 min longer than needed.
On those stations that get busy on crazy days, just don't plan your long meal right there. Drive to the next station. Or here is another idea. Go to the restaurant, get a table, order your food, then walk back and plug in. That cuts off 15 min.