*Random idea* Scrolls use Ritual-like powers but are usable outside a Ritual.
So imagine this, there is a Ritual that can cause an area to be purified by Holy-Radiant energy. This would normally be used for exorcisms and such.
However, since you inscribed the power into a Scroll it is usable in combat.
Thus this:
"As the zombie-hordes begin to swarm over the battlements and surround the party, the Cleric shifts his way into the centre of the party, the Fighter and Paladin raise their shields and keep pushing the zombies back as the Rogue and Ranger fire out from the protection of the shields. The Cleric begins to read out the Scroll (full-round action). As he finishes the Scroll burns away and light bursts out, the zombies around them turn to dust."