This is what I'd been doing: 1. Go to https://plus.google.com/circles https://plus.google.com/circles 2. The first rectangle before the listing of your contac

This is what I'd been doing: 1. Go to https://plus.google.com/circles https://plus.google.com/circles 2. The first rectangle before the listing of your contacts should "Add a new person" 3. Enter email address of invitee and hit Enter 4. Enter a name to associate with above email address, select Circle to add into, and hit Save I'm not entirely sure that this is the 'correct' way - I was just looking around for a place to enter arbitrary email addresses and this seemed like it. A couple of chaps I'd added this way got in, a couple more had to try a few times, and most of them see the "we've temporarily exceeded capacity" message.