I did this on my (previous)
Mk4 Ibiza. However the process would be much the same here...
The process was simply to remove the tailgate trim on the inside, usually a few screws too, plus the plastic clips (a good tug does no harm!). With the trim off, you will now find the rear wiper motor assembly is now visible. You need to unbolt this - after removing the wiper from the top first!
This will leave you with the hole in the glass, plus the water pipe.
The hole in the glass you can 'plug' with the rubber grommits that they sell in packs in Halfords.
The water pipe you can simply plug with some of the plumbers putty, to seal the end (stop it leaking).
(as you only cap the end with the putty, you can easily poke out the putty again in the future, should you want the Wiper back on).
To stop the rear wiper from trying to work, as said, disable it in Vag.com (when reversing with wipers on). Perhaps actually remove the rear wiper fuse too??
Does tidy up the rear end, and looks pretty sleek. Also the Leons suffer less from a dusty/dirty tailgate due to a different design to the
Ibiza (which suffered from this alot more).
Defo post up pics if/when you do this, would be great to see.