Mark Wallace is correct that this is primarily a people issue not a technology or Scrum-technique issue. Fortunately there are some people-techniques that work to resolve certain sorts of people issues. Your issue here is resolvable.
Daniel's answer touches (brilliantly) on the phenomenon here: that different personalities can have wildly different work styles and those styles are enduring and in many cases unchangeable.
You will not find a Scrum technique that will make a person change any of the unchangeable aspects of individual work style.
Here are specific techniques for harnessing the strengths of your visionary stakeholder while still getting useful work out of them each day.
Be realistic about what work they can and should do. Do not make any work assignment based on what you feel they OUGHT to be able to do, only assign tasks that they have shown they ARE able to do, or almost do (so they can stretch, grow and do).
Assess how this visionary gets his juice. Does it primarily involve them talking? Do they seem to need an audience? Schedule a daily brief talk with them where you act as audience. Harvest their good ideas. Keep this brief by using a timer.
Give the visionary the additional payoff of placing their continual stream of ideas into a visual Parking Lot. Sharing an idea that others ignore is a downer; sharing an idea and seeing it parked somewhere feels validating -- and frees the mind for the next thought.
Many visionaries hate to eliminate or rank ideas. Make him do it anyway. "We can only work on one thing at a time. Our priority from the customer is X. Which new idea is actually more important than X or should come prior to it? Why? What will we then choose to NOT do, in order to do this new thing?"
Hold this conversation near your visual tracking tool or Scrum board. Help the visionary see the current reality. Ask, "What can you personally accomplish today to move us forward?"
REMIND the visionary that doing the 2nd, 3rd, Nth awesome new idea they've spawned, is dependent on getting the 1st one done SUCCESSFULLY.
Look for clues, hints, and tells from the visionary's past and present, that show you how to get the best work from him. Does he need someone to pair-program with or talk things out with? Does he respond well to distant deadlines but collapse under the pressure of a shorter one? Do calendar reminders work? Gold stars?
REMEMBER that the visionary is an idea generator. Give him little problems to solve that are in his sweet spot, where the answer is not obvious. Think of him as an idea-hose, and point that hose at an area that requires a flow of ideas.
You can also set the visionary to work on diagnosing himself. Ask him to reflect on where and when he's been most productive. What was the work? What were the deadlines? What was the context and content? Aim his idea-hose at his own performance. (He's probably secretly just as irritated by his inability to sit down and crank out work as you are.) Keep the tone positive, relaxed, curious, accepting.
This topic is at the heart of an e-book I'm writing that's inspired by Drucker's "On Managing Oneself" -- excellent reading, available I believe at HBR.org and of course fine bookstores, libraries, and Amazon.