I would think that would be by having auto loans and making regular on-time payments. And having fully repaid loans.
One of those, "you have to have credit to get credit" type of situations, I believe. I wonder if mortage history affects it positively. They just told me in another other thread that other personal and student loan history don't affect it that much.
How can you improve your auto enhance scores
Have you read this thread about FICO Auto Enhanced Scores? It might give you some useful information.