As the vouchers are non-transferable, I doubt the Coupon Connection would help. My standing suggestion is to ticket a fully refundable itinerary for travel prior to the expiration date. You can then apply the value of that unused ticket to another itinerary up to one year after that. (I assume, technically, you could keep extending year after year, but that would probably be pushing the envelope.)

Also, I'm not sure whether DBC vouchers have residual value. If they do, and you can find a very cheap itinerary (try Paris to any TGV-station city in France!), you will get the balance back in a voucher good for one year. Essentially, you take a discount on your voucher, but at least you don't let the whole thing go to waste.