Ah, I see what you mean now. Although I still want to keep it open to all weapons, not just melee weapons. How's this:
Weapon Channeling
Prerequisites: -
Benefit: Choose one weapon with which you are proficient (e.g., Longsword). Choose one implement. You may use the selected weapon as if it were the selected implement. If the selected weapon has a range, it does not affect the range of any powers for which you use it as an implement.
I think that should do. I hope the language is clear enough, because I don't want anyone to think that this allows any new uses for implements. I guess that might just be a common sense issue.
Some issues I want to toss out:
1) Should I open this up to weapon groups instead of individual weapons? One reason I kept it to individual weapons was to avoid any confusing language surrounding proficiency; I want people to be proficient with the weapon they use as an implement.
2) Using it as an implement vs. limiting it to enhancement bonus benefits. I don't think this would be an issue, and it would be nice to keep it open to, for example, Elven Wizards using their bows as if they were wands, or whatever.
3) As soon as I can look up appropriate similar language, I also want to open this feat to being re-selected for other weapon/implement combos.