dont worry about it.... you can strap a heating pipe to one side of a brick and clip a cable to the other with no ill effect, the limited heat given out of a central heating pipe will cause at most a mild warming of the opposite side, i believe your over thinking this one or do you mean you want to lay bricks to suppress the heat .... forget it a decent gap is all you require, personally id only have concerns it the cable was strapped to pipe and then it wouldn't damage it too much -but you do need to have a set clearance, as your design current would change with ambient temp'