Jupe, I haven't read the passage in Armstrong your are referring to, but I think that you might be reading him too literally. He might be speaking more broadly about tactics.
An classic tactic is for several team members to join a breakaway group, so that, when they take their turn at the front, they ride slightly slower than the other attackers. This slows the breakaway a bit. Even if the other attackers notice, they face the choice of pulling all the time, or allowing the slowing to work.
I doubt it has to do with aerodynamics.
With respect to Richard's comment on the aerodynamics, many sources claim that the front rider gets a 1-2% advantage. That's so small that you'll likely not notice it.
Cheers,
Jamie