What you need to do is either manually create, or edit the VS2005 created,
proxy class file.  The problem is that Visual Studio 2005 doesn't create a
proxy file for a Web Reference until compile time.

For what you're doing, I suggest that you not add a WebReference using
Visual Studio's Add Web Reference tool.  Instead, run WSDL.exe to generate a
proxy class file for you.  You can create customized copies of that proxy
class, exposing only those features you need in your various consumers and
include the customized version in each build.

HTH