Use multiple email addresses in merge tag for recipient

I am trying to create a notification for BuddyPress that fires on a specific group event. The notification should be sent by email to all the group members.

In the Trigger->action() method I need to collect all the addresses and set them as a class property which the merge_tags() method can then access. However, currently I cannot use the EmailTag because it won’t validate an array of addresses or a comma-delimited string.

How can I set up this notification so that it sends to all group members?

Thanks.