Actually pulling this off is far beyond my technical capabilities but I was thinking it might be possible to use two 4GB cards working in tandem to simulate an 8GB card.  If it's reasonable to split the DAG into two parts each half could be loaded into a separate card.  Both cards could begin hashing together, passing control of the function back and forth between them as elements are selected from the portion of the DAG loaded in the other card.  As I said, the technical details of how Ethash works are outside my understanding, but as current mining software seems to lean heavily on pagefiles  and does use system RAM could a pool of pointers be shared between two cards allowing them to work together like this?

I understand this would half the overall hashrate, perhaps even worse due to increased overhead, but I think it's safe to say those of us with a lot of 4GB cards would prefer that to having a bunch of paperweights.

If my suggestion is completely absurd feel free to flame and carry on with your life.  My only request is that your insults are creative or clever   

-TBT