A standard way of using features not supported by your baseline platform but supported by later versions is to use the LoadLibrary and GetProcAddress routines to get a handle to a DLL, then get the address of the function, if it's present.
You can do this in .NET by using [DllImport], calling the function, then handling the MissingMethodException that results. However, throwing an exception is a relatively lengthy operation.
Junfeng Zhang reports that a new method GetDelegateForFunctionPointer has been added to the System.Runtime.InteropServices.Marshal class in .NET 2.0. You can now LoadLibrary and GetProcAddress, then construct a delegate from the resulting function pointer.