Updated 3/26: Pack is now compatible with the latest "Imperial Guards" DLC/Patch. Pack is in movie format. Delete any previous version from your NTW\Data folder, this will not overwrite; I changed the name to "Movie_AllBattleMaps.pack" to denote the pack file type it uses.
Didn't see anything like this available, so if someone has already done it, apologies.
This will make the MP only custom battle maps such as Waterloo, Austerlitz etc available to play in single player land battle mode.
*Installation* Use one or the other pack. First is a "patch" file, latter uses the Mod method.
Unpack the rar file using Winrar/Winzip/7zip/whatever packing software you may have that can handle rar files
Place the "Movie_AllBattleMaps.pack" file into NTW\Data folder (X:\Steam\Steamapps\common\napoleon total war\data)
Launch game, and enjoy.