Yeah, I'm looking for the same info, converting a Creative Map to Survival. If so you could make a Custom Map in Creative Mode and convert it to Survival before uploading it here for others to play on.
Here is a easy way to convert from survival to creative and it should work the other way.
1. Create new creative world.
2. Open %appdata%/minecraft/saves
3. Open save of the survival and create worlds.
4. Open both region files.
5. Take region files from survival and place into creative's region folder. (or the other way if you are making a survival map).
This should allow you to transfer maps between the two settings. You can always delete the old map in order to reduce clutter.