Saw this via on search in the forum, after asking support if there was anyway to do this.
He told me that there was no way to do that.
What is true is that there is no way to make such an email part of a follow-up sequence.

We are experimenting with an email that pulls several bits of data that are unique in each opportunity record.

It appears that the way to do that is to have the email generated by a trigger. We had thought of creating a follow-up sequence that would generate emails based on information in the opportunity record. Since that doesn't work, it appears that any email can only go out immedicately when the trigger is activated.