Connect LED Cinema Display (Mini DP) via HDMI
You don't need to use an adaptor (supposedly) -- thunderbolt ports are the same as mini display ports, so according to Apple you do not need an adaptor, because it "will work just like it was connecting to a Mini DisplayPort connector when plugging in directly to the Thunderbolt connector on your Apple computer."

That said, I am also trying to figure out how it works, because it doesn't for me currently. But it is "supposed to". 

Some links:

http://support.apple.com/kb/HT5219#11 

http://support.apple.com/kb/HT3382#3a