Then let them work on an editor and let customers make maps. They do not need to be directly portable ingame, but reviewing, importing and testing maps should be easier than create all from scratch.
When in doubt, make them "dream" sequences at first without ability to influence the rest of the game much (e.g. items gained there temporarily etc.).
And if they find a map they really like in that batch, they can ask the author and include it permanently or use it for events.