如何在一个解决方案中编写Light，Pro，Ultimate三个版本

I'd like to know how best to program three different editions of my C# ASP.NET 3.5 application in VS2008 Professional (which includes a web deployment project). I have a Light, Pro and Ultimate edition (or version) of my application. At the moment I've put all in one solution with three build versions in configuration manager and I use preprocessor directives all over the code (there are around 20 such constructs in some ten thousand lines of code, so it's overseeable):I'd like to know how best to program three diff