I have found a way to always start with a flame shock and use a /castrandom

/cast [target=focus-target,mod] [target=focus-target,nocombat] Flame Shock
/castrandom [target=focus-target] Flame Shock, Lava Burst, lightning bolt


this casts flame shock whenever I use a modifier like the ALT key or whenever I"m out of combat and starting a new fight.