5K 2017 iMac display rotation (180)

Hi there !

Does anybody know how to rotate display in 2017 5K iMac ? My iMac is too high for my desk. Previously I used 2011 iMac and mount it on VESA arm. My new iMac does not support rotation, and there is no chance to change it on VESA system if you did not bought it at once. The problem is that I had no idea about this situation buying it.

Do you know any third part software enabling display rotation? I plan to put it upside down. Thanx !