Job done for now with a glass bung from Halfords. I have a flush, glass bung coming in a few days off eBay to give an even cleaner look!
For anyone else doing this mod, take out the warning triangle in your boot lid, remove 2x T20 screws, and pull hard on the plastic trim to remove.
Pull small plastic cover at the base of the wiper arm, and remove 13mm nut. The wiper arm then pulls off, but will require a bit of force.
Next, undo the black clip on the little white cube at the end of your washer fluid tube, and pull the pipe off the motor. Unplug the plastic plug on the side of the motor. Remove 3x black 10mm nuts, and pull motor out.
Close your boot lid and remove the existing rubber seal, replacing it with your blanking bung/grommet.
Hope this helps anyone in the future that needs it!