The Macessity SlimKey V2 (no USB hub) is the closest you'll come. You have to take off the silicone feet. If you need to add 0.05" under the 27" iMac afterwards, whatever you put underneath (cardboard) will be 100% undetectable.
The only other option is VESA mounting both the display and iMac on arms and getting the VESA mount adapters from Apple. Due to the weight, you can't go for cheap arms.
Another alternative is to get a replacement stand fabricated for the Cinema Display. Since it'd be a one-off, i'tll easily be a few hundred dollars.
I have an ultimate 2011 iMac and a 27" Cinema Display myself. These are your options.