I have not been up close to an A2, thye are as rare as rocking horse s**t in Ireland. You may have read that we were going to buy one, but now the toss up is between a Polo GTI, WHY DID THEY STOP MAKING IT, and a Lupo, GTI or Sport. Got to get back to the MK II GTI feeling, ours is a bit dead at the moment.
Anyway, back to the point. Back in the 1950s SAAB put a slot in the above window rear spoiler oe the 95 to clear it. My Audi 100/A6 Avant has a slot in the above screen spoiler and the screen stays pretty clear. If the A2 spoiler is bolted on, similar to the MK II Golf, try spacing it from the rear screen with a few washers. Then go from there and devise an elegant solution. Let me know how it is mounted and I might come up with a solution.