As a PS3 user :

In a fate with one large boss you can use a macro : /Cure <tt>
That way you target the boss and whoever the boss is targeting you land a heal on her/him.
As side note the following macro is better for all situations (you can add mouse over if you play mouse+keyboard) :
/Cure <t>
/Cure <tt>
/Cure <me>

For fates with a lot of small mobs you can set your targeting to only players so switch between players and heal the ones with low health.