cable tv connection

[RUGMAN]

This is my situation, Had renovation done to my home, Plan on Tv mounted above new fireplace, electrician ran power and cable wire up to come out behind TV, mason came in and did a great job with stone face, Problem is electrician did not run a HDMi cable up there he ran cable box wire, My thought was to mount cable box on wall behind TV, this would not only get me a short shot of HDMI to tv, but also keep box out of site. Spoke to Metrocast, the person on phone wasn't sure that would work, said box is large 6inch x 8inch by 1 inch. I did not think that was that big, has anyone had a situation like this, Any thoughts??