Too bad AC hasn't introduced their one-way overseas fares. You are traveling in high seasons, at least in the summer, while just approaching the Christmas/New Years high season on the return.

Your best option seems to be buying a charter flight on ZOOM or similar carrier, and if you cannot purchase a return, the fare will still be cheaper and you can throw the return away. Same on the return. Unfortunately this does not help you earn Prestige [if you've done two returns to Germany already, you are likely sitting at about 16K status miles and need 9K more, which as you note, will occur on these flights if you flew AC or another STAR carrier.

You may have to bite the bullet as there seems little way around high fares for the dates you must travel. You might consult a TA that specializes in consolidator fares to Europe, but I haven't even been able to find anything cheaper out of BUF on UA or US.