IMac 2011 as external monitor

Hello there,

Im having a bit of a problem here, I have an iMac 2011 and recently got a macbook pro with retina display, this last one is faster and I want to use my iMac as an external for this. I have done this under OS X and it works with cmd + f2(with the imac's keyboard), but when I try under bootcamp windows won't detect the iMac's display.

So resuming it I can do it while:
macbook in os x + imac in os x = works.

But I can't while:
macboook in windows 7 + imac in os x.

Any advice welcome, thanks!