Sorry to say, but I’m still just not sure I understand what you’re saying. Just to be clear, this is what I had in mind:
1) Select the ‘not sent’ option
2) Filter by ‘unengaged recipients’
3) Create new list (name: ‘temp send’)
4) Send the email in question to the new ‘temp send’ list, but obviously DESELECT the ‘don’t send to unengaged contacts’ option.
Will that do it?