The late 2012 and 2013 27" iMacs had to be ordered with a VESA mount because they did not have the removable stand. However, there is a third party VESA adaptor available, which I successfully installed. I took a few pictures as I did it.
If you have the tools to get to the point where you can see the stand (through the iFixit guide mentioned), then you'll have the tools necessary to remove the stand. There are two possible exceptions. I found a flexible shaft screwdriver very handy (see step 2). Also, I used a metal file to modify the VESA mount adaptor mentioned in the parts (see step 6).