All right everybody, this was a tough and very subjective decision, because I personally liked all three solutions.
@ponts was thinking in 3D, @schwa found a solution I also had and @doughtaker was brave enough to suggest a similar solution to one of his earlier ones, which entails moving the pieces (which was not prohibited).
But as we can have only one winner and @ponts was the first one to send a correct answer, the reward goes to him.
Thanks again everyone for participating!