There was a post where someone explained this, specifically for druid's eclipse.
I read it at the time, but didn't understand it at the time, so didn't do anything about it, but yeah, it irks me to no end that my druid in same gear is doing 500dp less than my mage who has a 2 spell macro >.<

the action bar change suggestion is a good one (but indeed you can't apply that to everything)
cast spell1 > spell1 > spell1 > *ECLIPSE* > activate macro to change actionbar > cast spell2 > spell2 spell2.
best thing is that you don't need to retoggle it, you just proc the other eclipse instead.
Still a lot of micro management compared to FS LvB LB or Frostbolt spam


[Edit] ah, there you go, it was a post from Owltoid, who replied same time as me :-)