C# - Specify Range >2GB For HttpWebRequest In .NET 3.5?

I'm building this class to download files in parts/sections/segments. In .NET 4.0, I can use this code to specify the range to download from

long startPos = int.MaxValue+1;
HttpWebRequest.AddRange(startPos);

and it works because there is a long overload for the AddRange method. When I looked up the .NET 3.5 version, I realised the AddRange() method allows using int only. The possible workaround would be using the AddRange(string, int) or AddRange(string, int, int) methods. Since the class will have to work in .NET 3.5, I'll have to go with the string specification but unfortunately I can't seem to find any sample code that shows how to specify ranges using this procedure in .NET 3.5. Can anyone show be how to do this?As the first code sample I wrote shows, I would like to specify a range of type long instead of int. Using type int allows requesting for byte ranges only up to 2GB but long allows requesting for byte ranges beyong 2GB.

The question therefore is: How do I specify byte ranges of 2GB or higher on HttpWebRequest in .NET 3.5?