I don't know of any adaptors that would eliminate that situation. But I have used 2 cards situated lose together like that and had the same worry. Turned out, that the cards still got plenty of air flow and stayed cool. The top card DID have slightly higher temps than the bottom card, but nothing serious.
If you install a fan in the side panel, that would push cool air towards the card(s) and make a big difference, if you are worried. I have a 140mm fan in the side of my HAF 912 for just that reason cooling my 2 HD 6850s that are about an inch apart.
Thanks, I actually fixed it just 30 min ago! I went and bought NZXT front panel extender kit from microcenter and decided to try and cut the plastic connectors shorter, that way if I messed em up I wouldnt be ruining the actuall case ones. I removed the metal female plugs inside first and cut just above where the plastic tabs start to secure the plugs and shortened them prob a few mm. I had to do it to the usb connector that goes to the front panel as well. I then bent the bit of metal sticking out the top of the connector about 60-70 degrees and heat shrunk it. It was a huge success!! I now have the cards spaced apart and it lowered the cards temps by 6C top and 3C bottom at full load. What a pita they make these mobos for tri sli that dont fit full size cards in the bottom slot...oh well, I made it work.