Add function "add new contact to group" in Mail Version 5.1?

Just got my first new iMac and need support for it's buid in Mail Version 5.1.

My question for Mail Version 5.1:

For sample I get a new email from someone new. I want to add that person to my address book.

In Mail Version 5.1. I can click next to the Name/Email-Address and select "Add to Address Book"

Very good so far.

BUT I need a sub-context menue for let me choosing the GROUP to which to add the new contact.

Instead it adds the contact right away into the main defauld contact folder.

With having 6 main groups of customers in different languages etc. I need to be able to EASY add

new contacts from Mail Version 5.1. with one or two clicks to a certain Group.

How can this be done?