Inspired by this:

If a thief with ki focus proficiency (via a theme) finds herself wielding a ki focus enhanced dagger and an implement power that qualifies as a melee basic attack, does the thief get to add sneak attack damage dice? Furthermore, if she charged with this dagger-as-implement, with the feat "surprising charge" what damage would she add to her charge?

The wording of sneaky staff strongly implies weapon-only, and the coding of character builder reinforces that restriction.