I'm looking into this also. Uplift makes a dual monitor mount with a "heavy" option for an extra $35. I may give it a try.
Shop displays and mounts that fit your Mac. Hold your Mac with stands and docks
If you want to look for a monitor mount that can support Apple Thunderbolt 27" display, you need to consider two factorsâ€”weight capacity and VESA .
Apple Thunderbolt Display 27 a 1407 Aluminum Stand Monitor Mount LCD No. Thunderbolt Display A1407 27" Widescreen LCD Monitor w/ Apple Keyboard. vivo Dual LCD Monitor Desk Vertical Stand Mount Fits 2 Screens up to 30". (7).
Cotytech Dual Apple Monitor Desk Mount Quick Release with Clamp Base. Cinema Displays, Thunderbolt Displays Patented Replaces Apple VESA Mount .
FLEXIMOUNTS Loctek D5D Dual Monitor Mount, Full Motion Desk mounts 10"-
The Innovative iLift arm is a great choice for Apple Cinema Displays and the new Thunderbolt. Horizon Dual Monitor Arm for Heavier Monitors by UPLIFT Desk.