i had the same problem, but the only things that you can do (i think) is to check the file after n second using a timer, and do it again until the file is changed (or created)
you can do a /timerx 0 n $read/$exists that check the file every n second and stop it using /timerx off, or restart a new /timer 1 n $read/$exists every time that you check the file and it doesn't exists