Encontrei um post bem útil:
I've found a fix to a common annoyance I've had in Visual Studio. I always wanted an option called "Add Existing Folder" to right next to "Add Existing Item" in the "Add" context menu item in the solution explorer. It was always a long drawn out process for me to add a folder that already existed (renaming the folder I wanted to add, creating the an empty folder with the desired name through visual studio, then adding all of the files back into the newly created folder).
Instead what you can do is hit the "Show All Files" tool strip button at the top of the solution explorer, then right click on the folder you want to add and hit "Include In Project". Pretty trivial. Its amazing how long you can use a product and not know about all of its features.