use a rotating schedule :
Each get three days in a row using the parking spot, even days that they may not really need to. I wouldn't assign days of the week either, just start like today (Wed) Person A would have it today, tomorrow and Friday, person B would have it Saturday, Sunday, Monday Person C would Tue, Wed, Thurs Person D would have it Friday, Saturday, Sunday Person A gets it Monday, Tuesday, Wednesday etc....
Use a common calendar either on the refrigerator or use Google Calendar.
It is not okay for an alcoholic to get drunk once in a while.
So do not tell a food addict it is okay to eat like sh*t once in a while