Little tip. don't wait for the invite. Just refresh your G+ page and it'll popup when they open it. I've got in all of the three times I tried. :)
I was tempted to do my own but as I have as about as much visibility as an amoeba on a rubbish tip I don't think anyone would show up. LoL It is a big commitment as to work well for the users it would have to be in the evening at the same time every week.