Finally I managed to resolve the nuts' issue.
Here's an overview:

1.Remove the seat
2.Remove left and right assist grips
3.Remove the 2 tail covers
4.Unplug the 4 wire plugs and cut the 3 clamps of the tail wiring. (pict.1 )
5.Remove the rear fender (4 hex screws). (pict. 2 )
6.Remove the 2 muffler covers (optional)
7.Now you have all the necessary space to install the metal supports for the Givi holders. (pict 3 )
8.Install the holders just to test the 6 supports' correct alignment. (pict 4 )

Finished? Unfortunately NOT. Givi holders are touching the rear fender (and specifically the metal bracket) not letting it fit in its place.

Any ideas guys?
How about rubbing/filing a little bit off of the rear fender's metal bracket?