Bizarrely, a friend hit on the perfect solution: Playing 'fetch' on a longline. This hits the sweet spot of allowing the dog to dash off, but while keeping him under control.
An unexpected benefit is that the dog loves playing fetch so much, that he spontaneously runs back with the ball ready for you to throw again. Now that is what you call a win-win situation. By playing fetch not only his he burning energy but he's also learning to come back to you. Genius!
The answer is a game of "Fetch". The simple idea is to toss a ball or toy some distance away, have the dog retrieve it and drop the object into your hand ready to be thrown again. This has the genius result of causing the dog to run much further than you, hence tiring him out faster than you.
The equipment needed to teach any dog to play fetch is fairly basic, and the sort of stull you're likely to have lying around at home. It includes: