Welcome to the Lithium Community. I'm sure you'll find this a very useful place.
I'm not sure if you can achieve what you want to do, but I would guess that the vast majority of communities would use $user.login (username) as that's what community members are generally going to be referred to on the community - that's their chosen "name".
Also, have you made completing the first name field when registering mandatory for community members? If not then obviously using the first name might not be a great idea for the notification.
Jason
