I have examined one of those climatronic units out of a Golf and there is not an actual mark anywhere on it to indicate the correct spot to place the hose. I was looking for some circular marks anywhere on top of the unit that would indicate where a hole was to be drilled- maybe someone with a Passat can chime in.
Logically, as the glovebox duct pipe has a right angle on the end, (and looking at the ETKA picture and also in ERWIN workshop manual), it should go in the top. As previously noted this would be virtually impossible to drill in situ, as there is only about 1" maximum clearance above the unit when it it installed in the car.
Also if it was mounted low down on the side, there may be an ingress of actual water into the pipe from condensation after the car sits for a while, for example (or the drain hole gets blocked!). Looking at that Audi site link though, it is fairly low on the side...I didn't really check the box around that location, so there may be something in that area...please check!
To only get cold air ducting, you would need to place the inlet after the evap coil but before the blending box from the heater core (as previously noted).
You can see that the evap core is mounted at an angle thru the box and the molding of the box on top shows its orientation pretty well. Where it slopes down to the heater blend box it would be clear under that.
While you have the unit out why not split it apart and check - and take some photos for us all.
(especially looking straight down with the top off!)
I am keen to do this as well on my (right hand drive) Golf. I already have the hose and valve but struck a bit of a dead end with finding the correct location for the hose too.