I received a mail message sent to multiple respondents. How can I add all of them to my address book, without having to add each of them separately?

Workaround:
Copy all recipients to a text editor window and convert them to a CSV set. Create a new address book and tell KAddressBook to import the set.

However, this raises the following question: how can I set a category on multiple selected contacts at once? Because it seems to be the only way to get them all into KOrganizer’s participant list.