This might be killing a fly with a shotgun, and it might be that I'm not understanding your problem correctly...I'm just trying to think outside the box.
Have you looked into using extension mobility to solve the problem? I think that if you created a profile that had a shared line appearance with the emergency phone, then when the bell went off someone could log in to their phone with a well known profile and now have the ability to answer that phone. This is actually much more configuration per phone than using a Call Pickup Group would be...the only advantage I see is that if you needed to put some phones in a Call Pickup group for some other reason, you would still have that as an option.
Let me know if I'm way off base with that idea.