In the Wiki for debugging native code mdl application it mentions being able to attach to the microstation process and then select the dll to debug as follows:

Debugging the Application

Once connected to the MicroStation process, you can add the application to debug. The first step is to include the application's DLL. Select Project > Settings, and select the Debug tab. Change the Category option to Additional DLLs. Select the application's DLL and click OK.

I cannot find where this option to select the additional DLL in Visual studio 2013 is.

Ray