Hi there,
I don't think I have stumbled on a gouge or prep course like the pilots have but from personal experience I would say the following.
I believe the hiring and interviewing process is pretty similiar across the board at LUV, so more than likely your relative will be facing a written test and then 3 1 hour interview sessions with different indviduals like HR, a mechanic and maybe his potential supervisor.
I also believe system wide they look for the same characteristics, be yourself, be yourself and did I mention be yourself. I think if he just relaxes and realizes that, this is the last aviation job he'll ever have, he'll do fine. Also tell him to excercise some patience, I've been in a hiring pool for 13months now, interviewed 15 months ago, and applied 18 months ago.
Great company but everybody else knows it too, lol
Good luck.