A macro is not allowed to constantly queue up an ability anymore, you've still got to hit the macro button each time you want to use it. Which is why a lot of tanks combine Devastate + Cleave/Heroic Strike together as you'll always be able to hit Devastate (no CD) and each time you hit it you'll also trigger a Cleave/HS.
I think you're looking for a toggle that allows you to hit it once and convert all white swings to Cleave until you toggle it off, if that's the case, you won't find one.
Jalousie: Two ovaries walk into a bar.
"Hey, can we get some cervix over here?"