[gokhan]

Create an empty circle. Add them by their emails. Post to that circle, G+ will send a "X shared Y with you" email which is actually an invitation.

Does this work for you?

[MattJ100]

This hasn't worked for a couple of days at least. Yes, the invites go out, but the signup page only intermittently accepts logins (presumably as they open/close the floodgates).

[gokhan]

I just joined G+ 2 hours ago with such an invite.

[sonnekki]

I must be missing something. When I select the 'view post' on the invite email, the interface tells me that I need an invite. Quite a conundrum!

[vinutheraj]

Keep trying. Didn't work for me 2 days ago. Worked today.