I do not think this is an automatic way to do this. You can simply create a new website in Visual Studio and copy the files from the web application to this new website. Be sure to go into each .aspx / .ascx file and edit the "Codebehind" attribute so that it reads "Codefile" (the codebehind directive must be compiled and therefore will not work on the ASP.NET website). You will also need to delete the Designer / Designer.cs files.
I hope you do not have too many files so that it is not too much PITA.
source share