I'm with Desmophiile here, you;d be putting your life in the hands of strangers and relying on their common sense and riding skill and, as they sadly prove every year, some muppets have little of either. on parts of the course, not just the mountain, you would be running on the road at the exit of blind bends with riders exiting at 100mph plus with nowhere to go. I had a 'non trivial moment' a couple of years ago when a trials chair outfit decided to do a neat circle on the road out of the layby at Joeys - I was going steady and managed to avoid him but the two bikes up my inside missed him and each other with millimetres to spare,

I suspect that if you tried it some caring manx coppers would explain the error of your ways and give you a lift to signpost.

If you want a challenge try running the Parish walk route that'll keep you out of trouble for a few hours