Solo/Co-Op Issues

It's it possible to get more than 4 people in a session of solo/co-op ? I know there's portal but while we're in game I just want to just jump in. It's kinda limiting not letting more than 4 people in one session especially when we're a group of about 8 people playing. Some of our friends have transitioned from COD to BF and we're trying to help them get a grip in the game.