This will work for one time use. To create a mailing/distribution list for later use, you will have to create a new group in Contacts/Address Book and bring the addresses over one at a time - or use Automator to create a script that does it for you.
Another option would be to save a blank email (after you paste the addresses in the To/Cc/Bcc field) as a draft and use that as a template each time you need to send out an email to these people. Tedious, but OS X's native mail client isn't very good.
