Hi, rivrod,
When I walked the Camino de Madrid, I had two companions for about 5 nights, and the rest of the time I was completely alone in some beautiful albergues, so I can't imagine anyone is going to care which way you are going.
Walking backwards is a different story, IMO. On the Frances to Sahagun, there won't be a problem, because of the huge numbers walking towards you. But on the Madrid, I think it could be tricky. I'd bring some good maps and a compass. The good thing about this camino, like most of the caminos, is that you are never far from civilization (except maybe for the day between Cercedilla and SEgovia), so even if you get lost, you will wind up in a town nearby and can reset your bearings.
Buen camino, Laurie