Andrew_Allston - I have just checked and your organization was whitelisted/accepted into this preview last week on Wednesday 08/23 so the feature should be enabled on your tenat. You should have received an email from us on Wednesday. Please submit a bug so that we may track your issue.
Throughout the Skype for Business Preview program, you will be able to get support on the features that you are trying out. To get support, login to our preview portal www.skypepreview.com , select Report an issue and use Create New Bug option to report an issue. Once a ticket has been created, please respond to this email with the ticket number.
Please note that support engineers are available to provide support from Monday – Friday, between the hours of 6 AM – 9 PM EST. Requests outside of those hours will be triaged the following day.