Assuming the cable is running along the exterior wall.
1. Painting the cable to match the flooring or mopboards.
2. Change the cable to another brand/color to better match the decor.
3. Floor length drapes (even false drapes) for improved room acoustics AND hiding the cable.
4. Building a false wall, or casement, covered with decorative fabric or wallpaper. The false wall, if built deep enough, could be waist high and used as a shelf planter or storage.
5. Find a new girlfriend, one that is a professional interior decorator, and let her redecorate the room. Didn't say you had to keep her. Just be friendly while you get your loft redecorated for free.