I'm not sure if this would work but...

/castsequence [target=Player] cleanse, [target=Party1] cleanse, [target=Party2] cleanse, [target=Party3] cleanse, [target=Party4] cleanse

I don't know if this macro would even work, but if it does, you're at worst 5 clicks away from cleansing the correct person. This is assuming there's no negatives to attempting to cleanse someone who doesn't need it. (i.e. you get a "nothing to cleanse" popup and no mana loss.)