MBP'13 (Late 2011) Win7 (BootCamp) + iMac'27 (Mid 2011) as an external display? Is it possible to use iMac'27 (Mid 2011, MacOS) as an external/target mode display for the MBP'13 (Late 2011) running Windows 7 in Bootcamp?

I'm using thunderbolt cable.

It works perfectly fine if MBP is booted into Mac, but Win7 can't seem to detect external display. Command + F2 on the iMac does nothing.
Yes. You have to reboot the machine into boot camp with the display already connected. 

See apples KB article here: http://support.apple.com/kb/HT3924 (bottom of the article)