I played with it a bit. If you spam it fast, it never does a heal. ;(

Here is my current one:

/assist focus
/castrandom [target=focus] lesser healing wave,,
/castrandom [harm] lightning bolt(rank 1), earth shock, lightning bolt, chain lightning,,,,
/startattack

You can play with the commas on the end, or swap the order of harm/heal to fine tune it to your liking...



to go with my melee:

/targetenemy [noexists, harm]
/cast stormstrike
/startattack
/castrandom [exists,harm] lightning bolt, frost shock, chain lightning,,,