After buying a 1989 Audi 200 Turbo on ebay I drove it home and did the easy maintenance, like Oil change and air cleaner element. Or so I thaught. You are right, that air cleaner is a real pain. After removing the obvious parts around it I found that taking out the right headlight assembly gave me enough access to get to the filter.
That sounds crazy, but worked.
By the way, in the Bentley repair manual it just says: "We recommend that you have the air cleaner serviced by your Audi Dealer..."