I only go into big rig fuel stops, and advise the cashier that I'm going to go in backwards (i.e. I circle around to the exit side and drive into the bay outlet, having first set a small traffic cone in the entrance to keep it clear until I can pull in.
After I fuel (I can fuel from either side), I pace off the distance I need to reset the cone at, so that I can pull up with the DEF tank adjacent to the DEF pump.
Some fuel stops require two separate transactions.
I carry a store-bought jug in case I get caught with no DEF in sight, but never use it, except to replace it with new near the end of the season.