My first thought: you can't.
My second thought: well, take a page from Barry Boehm's spiral method and a page from agile, and mash them together with an implementation plan, and maybe there's something to be done.
There is a natural tension to be addressed: the creative mind wants no boundaries; the management mind wants order and predictability.
From agile: take a white board and a dart, and begin storyboarding or other creative activity.
From spiral: from the starting point, build outward in cycles, addressing a new point with each cycle with an objective of getting the right pointing vector for the implementation phase.
Back to agile: box the available resources so that something useful is more or less a certainty. After the whiteboarding and spiraling about--so called iteration 0 where no operational deliverable emerges--use one of the boxes to plan out the mechanics of implementation. It's expected that you'll begin with 10lbs to go into a 5lb box, but after creative iteration, you'll come up with 5lbs that is useful and worth doing.
Then: do it!
Then: DONE [when you have a deliverable that is useful and operational]
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