Targeting .NET 2.0 & 4.0 in web.config

[Weenuedic]

I have a web application that usually runs with a .NET 2.0 AppPool account. But because the AJAX calls posts string serialized XML to the server, I needed to add the "requestValidationMode" option to the httpRuntime setting when running the same AppPool account with .NET 4.0.However, switching back to .NET 2.0, the application responds with error with regards to the "requestValidationMode" option.Is there a way one can have one web.config with some conditional mark-up so one need not edit the web.config each time the version of .NET is changed for the AppPool?Any help would be greatly appreciated.