Unless you have a pressurized sprayer (like JETaah) or similar device, you are stuck using gravity to fill the transmission.
I have used the official VW fill tool (adapter for the transmission drain hole, 10 foot long hose, and adapter to connect onto a 1 Liter bottle of transmission fluid) and I have used the "Herm-o-fill" using a hose to fill through the fitting for the transmission filter. The top fill is the MUCH better choice of the two.
Regardless of the method used to fill, I always add 5 Liters. The procedure to check the level will drain out any excess, so I don't worry about adding 4.5 vs a full 5. As long as some excess drains out I know I have the correct level.