How to get lazy loading using PLINQ?

One of the nice things about linq was that endless data sources were processed lazily on request. I tried to parallelize my queries and found that lazy loading was not working. For instance...

class Program
{
    static void Main(string[] args)
    {
        var source = Generator();
        var next = source.AsParallel().Select(i => ExpensiveCall(i));
        foreach (var i in next)
        {
            System.Console.WriteLine(i);
        }
    }

    public static IEnumerable<int> Generator()
    {
        int i = 0;
        while (true)
        {
            yield return i;
            i++;
        }
    }

    public static int ExpensiveCall(int arg)
    {
        System.Threading.Thread.Sleep(5000);
        return arg*arg;
    }
}

This program does not give any results, apparently, because at each step it is waiting for all generator calls to dry, which, of course, never. If I pull out the AsParallel call, it works fine. So, how do I get a nice lazy load when using PLINQ to improve the performance of my applications?