Bi-directional A-B-A coast down tests or bi-directional A-B-A tests with a cruise control. Also you can look at what others have done that has worked, many of which have put in wind tunnel time. If you look at the book that gets quoted on here a lot by Hucho, there has been a lot of testing done, and lots of it back in the 1920's. Although the data is old, the same principals still work... Smooth flow around the vehicle is still better than turbulent flow. Do a search for user Aerohead, he has lots of good articles posted in his AeroDatabase.
HERE is an example of some of his stuff compiled by another user with links.