There is nothing that I'm aware of that will do this for you out of the box in Marketo.
One of the things we've done in the past is to create an email alias and have everyone who sends samples to always include the alias so that we can know what samples are being sent and at what time. Although, it wasn't very helpful because nobody was really using it.
Another thing was that we created clones which helped keep the reporting separate. During test phases, we would use live records or seed lists. Then, when it was time to go live, we would clone the email, fix it up a bit and then send that one instead.