As far as I know that isn't possible... unless someone created a plugin. The problem lies in protecting the project. The way Visual Studio works it has all source code outside of the project file so a plugin would have to take 1 file with all of the encrypted data, decrypt it somewhere and let Visual Studio open it. Then it would have to re-package all of the data and remove the temporary files when Visual Studio exists. I'm not sure that that's possible.

Why do you want to do this? There may be a better solution.