Spray the insides of 4 microwave-safe mugs with cooking spray.
Spoon 1 teaspoon grape jelly into the bottom of each mug.
Whisk cake mix and peanut butter together in a bowl; add whipped cream and egg substitute and whisk until batter is smooth. Divide batter evenly between the mugs.
Place 1 mug in the microwave and cook on high until cake is set, about 1 minute, 15 seconds. Repeat with remaining mugs. Invert each mug onto a plate to release cakes.