Using WriteOnceBlock from TPL dataflow? There's got to be a better way!

gistfile1.txt

public async Task<R> ExecuteAsync<R>(Command<M, R> command)
{
    var completion = new WriteOnceBlock<object>(_ => _);

    _commandQueue.PublishEvent((e, i) =>
    {
        e.Transaction = command;
        e.Result = completion;
        return e;
    });
    return (R) await completion.ReceiveAsync();
}