I have, relatively easy job. bought a wiper delete plug from ebay like this - (
https://www.ebay.co.uk/itm/Porsche-996-Rear-Wiper-Delete-Plug-Billet-Aluminum-Anodized-Plug-Black-Satin-/320901389552).
Remove wiper blade arm.
Then from the inside remove back panel under the windscreen and remove bolts and plugs, you'll need to angle the motor around a little to get it out. - removal done in 15mins.
took 20-30mins to put in plug mainly because it kept moving, i'd suggest a second pair of hands to hold stuff in place.
Ensure you have some sealant (i used clear aquarium sealant) to seal the rubber washer to the body.
ensure you have some lock tight to hold the nut in place on the plug.
its a good 6 months since i did mine but if i can do it then anyone can.