This has been discussed in an old post which can be found by searching for formations here in the forums.

The easiest way to do it in my opinion was stated by Zaelar

Quoted by Zaelar - Two buttons. One is strafe left for alt A while strafe right for B, other is same for C and D. Press both buttons, but hold one for longer. You'll end up with(assuming you start with main and four followers):

- -M
A A A A
and if you would like to read more of the discussion about it the thread is here Spread Out Macros/Formations