Have Marty impersonate Marty Jr and tell Griff no
From Create Your Own Story
You give Marty future wear to help his disguise. Marty changes into 2015 clothes, power lacing shoes, an adjustable jacket and pants wore inside out. You send Marty to the Cafe 80s to await Griff. To make sure Marty Jr doesn't show up, you go to intercept him.
You track Marty Jr down and use the sleep inducer on him. Unfortunately, since you used it on Jennifer, you don't have enough to knock Marty Jr out for a full hour. Marty Jr gets up and continues to the Cafe 80s.
What do you do:
