Code:
/assist focus (or make your /castsequence [target=focustarget])
/castsequence rest=target/combat slow, scorch, scorch, scorch, scorch, scorch, fireball, fire blast
This macro would assist your paladin and then slow, 5x scorch, fireball, fireblast... after being pressed over and over... anytime you leave combat or switch targets it goes back to slowing the mob then scorching.