It's open to DM interpretation but the feat Distant Vengeance in Dragon 382 can make an invoker ranged basic attack at-will in to a strong option.

Spoiler: Feat Text
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Prerequisites: Avenger, oath of enmity power
Benefit: As long as you are within 10 squares of
your oath of enmity target and no other enemies are
adjacent to you, you gain the benefit of your oath of
enmity on all ranged basic attacks against your oath of
enmity target.