Honestly... I'm not sure you can, outside of buffing raw potency of WHM tools (which you "could", but then it'd suffer like MNK does). PLD is a separate can of worms not meant for this thread, but I'm honestly not sure how they could really give WHM its job without completely overtuning its numbers in comparison to the other two jobs. WHM is a pure healer, and offers no other utility to the group (which is core for progression, but outside of that is useless).

I don't know, just my thoughts as I sip my morning coffee.