Our Templar in the group wants to have a spell-like ability akin to the smite evil ability of a D&D 5e paladin. What I came up with was using an Augment magic action to add weapon effects to his current weapon. The downside is that it requires an action to produce the effect and concentration to maintain. Here is what it looks like.

Divine Brand
Magic Action : Augment
Effects : None
Range : Engaged
Concentration : Yes
Action : Make Easy ( ◆ ) Divine check. Success: Add 1 effect to your melee weapon’s attacks until the spell ends.
Effects
Fire : Gains Burn rating equal to Lore.
Holy : Against undead and Ynfernal targets, each uncancelled success deals +2 damage instead of +1.
Deadly : Your weapon’s Critical rating changes to 2.
Additional Effects
Additional Effect : + ◆ per additional effect.

Overall, this seems less efficient that just running up and hitting things. Does anyone have thoughts or suggestions?

I would suggest making it a talent, possibly having Templar as a prerequisite, that gives him a unique Augment additional effect that he can cast on himself or others. I would personally keep it simple and just add the Holy/Unholy effect from the attack spell to the target's melee attacks. Perhaps have an improved version that can add the Burn effect (to undead/demonic targets only, perhaps), but reducing critical rating is already covered with the Wraithbane talent.

The justice of the citadel talent that lets you add ranks in disciplin to damage has some what of a smite flavour but in addition to that this is what we use.

Smite evil
Prerequisite: Your character must have purchased the
Templar talent to benefit from this talent.
Tier: 2
Activation: Active(incidential)
Ranked: yes
When making a meele combat check your character may
spend a story point to add the breach 1 quality to the
next attack. This may be done once per session for each
rank of smite evil