There are too many conflicting interests on the glen and it's a natural beauty spot. I can't imagine the council agreeing to you digging or marking any trails over it. Even if they did want to discuss it with you, which is very unlikely, their first question will be something like "what previous experience do you have in marking and building trails?". "do you have liability insurance?". If you have no crebible background, they'll not take you seriously. Personally, I would just carry on enjoying riding and discovering the natural stuff that is there. If you start stiring up trouble for the council, it could spell the end of things like the little jump quarry etc.
Try putting the question on the SingletrAction website forum, they are local riders and people on there have lots of experience dealing with land owners and access, but expect to be shot down on your idea.