To get to the fuel sender, just pull the back seat cushion up. You will see a round cover held in place with screws. remove the cover, and you will see the top of the fuel tank where the fuel pickup/sender is located.
Check the connector. You can then remove the pickup/sender and see if the sender is stuck in the full position.
I would run tank down to a minumum of fuel and drive the car down an extremely bumpy road. I would try stopping very fast and turning back and forth and anything else that might help to dislodge this sending unit. A half a tank of fuel may add the "slosh effect" to the degree that the tank baffles allow. It could help alittle. Maybe a full tank with very bumpy driving with lots of fast turns, ect would assist even more. I would try anything to avoid accessing the fuel pump/sending unit access port on top of the fuel tank under the access panel on the floor under the rear seat. The current from that sending unit should be checked to make sure it is the actual sending unit and not the guage on the instrument panel that is at fault...VW knows all the spec for the full range of fuel levels from bone dry to full. Good Luck, JK