ThreadPoolTaskScheduler.cs

protected override void QueueTask(Task task)
{
    MutateState(task);

    var newScheduler = new ThreadPoolTaskScheduler();

    typeof(Task).GetField("m_taskScheduler", BindingFlags.Instance | BindingFlags.NonPublic)
        .SetValue(task, newScheduler);

    ThreadPool.UnsafeQueueUserWorkItem(t => newScheduler.ExecuteTask((Task)t), task);
}

private void ExecuteTask(Task t)
{
    TryExecuteTask(t);
}