Daggers (and possibly other weapons) as implements

I have a sorcerer who uses a Winged Dagger +1 as his implement/weapon. It works fine on all his weapon powers, but I'm having a problem with his implement powers. It looks like if I mark the power as using the dagger as an implement, it's also adding in his weapon proficiency bonus on the attacks, even on pure implement powers. Is there a way to fix this? Or do I just need to do something like put a staff with the appropriate pluses on it and have FG think he's using that for implement powers so that everything maths out right?

Yes, I would say the easiest way is to create a copy of the Winged Dagger +1 and set it's proficiency bonus to 0 and point the implement powers to that instead. But I am surprised the 4E ruleset does not already take that into account by looking for the Implement keyword.

That's what I ended up doing, but I was also surprised the ruleset didn't handle that (unless I'm doing something wrong).