I have to acknowledge, it has probably been more than a couple of years since I have done any real DNN (formerly DotNetNuke) development. Quite a few things seem to have changed in this time, especially with DNN 7.x.
I do not have much time to provide the background, suffice it should be to say that I decided to adopt ASP.NET 4.0 MVC Web Api in a major way today after being in evaluation mode for some days (4.0 MVC was still in Beta as I wrote this).
And so I needed to convert my existing Web Application (WAP) projects to Web Api projects. And I followed a very simple approach to figure out the same. I created a new solution with 2 projects, one a WAP project and the other a Web Api project. I removed all default configuration from both the projects leaving only the absolute essentials behind.