Customising the default AppSettings and ConnectionStrings Expression Builders

I have been developing applications for almost 30 years - started with early versions of Basic on the Sinclair ZX80, moving up via UK101 and Amstrad to PC. Played with Assembly as well. First big application was for a complete test set, which was written using QuickBasic (all I had available to me). Moved on to a bit of C and C++ (never really got to grips with them) and then 11 years ago, got into Visual Basic/SQL Server and HTML. Moved onto .NET and then in the last few years changed across to C# when the job market indicated that it would be better.
Have now developed quite a few ASP.NET Applications, and along the way have played with WPF, Silverlight and am currently working on an MVC based application.