AbdulAlhazred
Legend
I thought that this was made unambiguous on PHB225:
The whole bit about the Implement and Weapon keywords is about when to apply the enhancement bonus to powers granted from another source, usually one's class, paragon path, etc.
I disagree. These keywords tell you when the attack IS delivered through the item. Unless a power has an accessory keyword the power isn't being delivered through the item and thus PHB p225 simply tells you what to do when the appropriate keyword is present. In the case of the OP's question by RAW the power isn't delivered through the weapon because it isn't a weapon keyword power. The power is GRANTED by the weapon, but that's a different thing.
In fact there is actually no rule which says that a power granted by an item has to be delivered via that item at all. That may have been the designer's intent but by RAW if I have a +1 Wand of Fiery Bolt and a +6 Magic Wand no rule prevents me from using the Fiery Bolt power of the +1 wand and delivering it via the +6 wand for a +6 enhancement bonus. All I need to do is use both wands.