Create an email script token to show a date 7 days prior

We send reply looking emails to subscribers who do not respond. We currently use a {{my.send_date}} token to display the date the original email was displayed. We're taking this same method and applying to an email stream. Because it will be mailed out at various times, I need to create a token that will make the sent date 7 prior.

I'm trying to change the date to 7 days in the past. what would I need to create to do this? I'm sure it's probably an email script, but not sure where to begin.

Best regards,

Donte