This is for Visual Studio 2008.
I have Tools|Projects and Solutions|Build and Run|On Run, when projects are out of date set to Always build bec
I found it convenient to create a new build configuration in order to do this.
Right-click the solution in the Solution Explorer and choose Properties. From there, choose Configuration Properties / Configuration. Now choose Configuration Manager and create a new configuration as shown. You can create the build configuration as a copy of your Debug project:
Then, press OK and turn off all of the project build flags:
Visual Studio will have created a folder underneath the bin folder in the startup project with the name of the new configuration. Copy your pre-built files into there and run the new configuration.