I think this is a new opportunity since the question was asked, but now you can create a video call button that launches a video call with a list of invited users (based on the G + profile ID, G + circle ID, or email address).
See https://developers.google.com/+/hangouts/button#invite_parameters for more details.
Note. A list is just an offer to a person starting a video call. Before starting Hangouts, this user can skip the invitation or change the list of people.
source share