I'm not aware of the situation with the newest iMac (late 2012) as we have the previous model. There is useful information on the "macrumours forum" found by searching "how to put the stand back on iMac" should the plate with the 8 screw holes to which the stand attaches have disappeared into the back of the iMac. Also on YouTube.
I have successfully removed and replaced the stand on my iMac and would make the following observations/recomendations:
1. I would recommend using spot of a thread sealer, such as Loctite, on the 8 small screws when replacing the stand, taking care not to over tighten those screws.
2. I was unable to release the latch to move the stand back into the iMac using the thin credit card piece of plastic included in the VESA mount kit sold by Apple so, I used a chefs palette knife (used for spreading icing on cakes) and was able to release the latch on the first attempt. This knife has a wide round ended metal blade a little thicker than the above mentioned plastic card. CARE SHOULD BE TAKEN TO INSERT THE KNIFE AT A 45 DEGREE ANGLE POINTING TOWARDS THE TOP OF THE IMac NOT MORE THAN 20 to 25 millimeters INTO THE iMac, GENTLY FEELING FOR THE CATCH. The latch is in the middle of the slot.