1) The brake cleaner or Vodka are solvents. Sometimes the rear oil seal leaks in tractors and contaminates the clutch disk. The oil turns to a very tacky grease causing the pressure plate and the clutch disk to stick together. As solvent can clean part of this mess and bring the clutch back to a usable condition. Tying the clutch pedal down or blocking it down while parked will also help. However, the proper fix is to replace the rear seal and clutch. Solvents will do little for a rusty clutch.
2) If the clutch has set for 10 years, rust is probably the problem. Some of the ideas presented are pretty extreme. I would never chain a tractor to a tree. You can break something that way or injure someone. I like the idea of using an implement such as a plow to create drag once the tractor is moving. Even if you get the clutch to break loose, you will never get it to engage properly due to the rust. Proper repair is to replace the clutch.
If we are talking about the 8N you have listed in your profile, it is such a basic tractor, and small, that separating the tractor should be doable.