When adding a user control or a project reference to a VS 2008 C# project, I can add only one configuration of the assembly. Is it possible to add separate configurations, d
Instead of adding reference to a .dll directly, which forces you to choose between the .dll from debug or release folder, you should add reference by choosing 'Project reference'. This link explains how to add reference through .dll vs project-project reference. For your purpose, you should choose the latter.
Also refer to my answer to know when to add reference as a .dll vs reference as a project.