Well, based on the entry under Staffs on pages 240 and 241 of the PHB it looks like you are able to use powers tagged to weapons so long as the class you are using allows for the weapon to be used as an implement and the power involved has the implement keyword.
The wording doesn't seem to restrict the use of the weapons powers at all, so for all intents and purposes it should act exactly like an implement when it is, in fact, being used as such.
The example you've used seems a little weird (dagger using wounding power at range), but unless the rule is addressed elsewhere it seems like its kosher.