The simple answer to this is "You Don't" (unless you have a TTB/ATF License). However, here's why people successfully ship samples all the time without being sent to Guantanamo Bay: The Government Jack Boots don't have the resources to go after everyone, so they concentrate on people who have money. Some guy shipping a few samples out of his basement doesn't have money, so they ignore him. The guy shipping ten thousand bottles has money, so they kick his door in and shoot his dog.
The key is not to slap them in the face with a dead trout. Or a live one either. As long as you don't basically force them to take notice (such as by shipping a leaking container by USPS), they will pretend they never heard of you.
I once asked the TTB if it was legal for me to advertise beer on tap as part of a rental listing for my spare rooms. Answer, in e-mail from a TTB agent, "No. Although, the advertising itself isn't really the problem. It's that you're essentially selling alcohol without a license by making it part of the rental deal. However, in such a situation, if you had a communal grocery bill for the house (1 gallon of milk, a dozen eggs, 50 pounds of grain), there would be no way we could legally prove you made beer with that grain and not bread." So the guy charged with enforcing the law is telling me how to skirt around the law.