I think the problem is that the 'target' of the spell is hardcoded.
You can change what it does, but not who it does it to.
The only way I can imagine it working with my limited knowledge of NWN scripting, would be to make it affect everyone nearby, giving them the bonus. (Imagine a Bless, but instead of +1 AB it improves Pick Lock by the appropriate amount)
This could work, since there's rarely going to be a situation where many people with good lock pick is a significant advantage to one person with good lockpick.