3 viable targets using /targetlasttarget and /focus?

Application: Setting kill order for instances, swift change of targeting in arena

Prior to a pull (or prior to battle in arena), first set a focus for your characters, then set a target, then change to another target. Theoretically, using /targetlasttarget and /cast [target=focus] you should be able to change seemlessly between the three, since you will never target your focus, the target and lasttarget keep switching places.

Has anyone tried this yet? I'm trying to work out a new system for my new team.