Can I create new triggers?

Is it possible to create new triggers for emails sent by the Buddypress Group Email Subscription plugin?
There’s nothing in between “All Emails” and “Daily Digest” except the “New Topics” setting which seems to apply to Forums with bbPress only. I’d really like something equivalent to that, but for ordinary Buddypress activity streams without bbPress forums.
i.e.
– send email notification immediately when there’s a new post
– don’t send email notification when there’s comments or replies, as this would be too many emails

The “All Email” trigger sends email for EVERYTHING, including comments and replies. I’d like to reduce the volume of sent emails, but still have new posts trigger an immediate email.
TIA