Just a hole straight through the glass mate. Its simple, but you need a bit of patience to get the actual arms off the splined fixing as it will more than likely be seized.
to cover the hole you can either use a rubber grommet from Halfrauds, or go to a local pug garage and get these:
874542 - Plug
874543 - Washer
874544 - Screw
£2.32 it cost me