Not sure if it is the default setting, but T switches the target to your target's target (wow, that sentence..xD).
So as a healer, for example I go:
1 (cure) - 1 - 1 - 6 (Cleric Stance) - T - 7 (DoT) - 8 (other DoT) - 6+T - 1, 1, 1..and so on.

There is no option to automatically cast on your target's target, but through macros and the manual use of T, it's still very easy and does not involve clicking or circling through targets.