Change the way how HttpValueCollection encodes the arguments

    var original = "АБ";

    var query = HttpUtility.ParseQueryString("");
    query["Arg"] = original;
    var tmp1 = query.ToString();

The code above (which is the recommended way of building query strings) encodes the argument as Arg=%u0410%u0411
However, the target API doesn't accept this argument and demands it to be encoded this way: Arg=%D0%90%D0%91
How can I make HttpValueCollection use this encoding?