To fill the marshmallow creme without a piping bag- Use a butter or paring knife to make a small incision into the bottom of the cupcake, about 1/2 inch, give the knife a full 360 degree turn to form a hole in the bottom of the cupcake. Place the marshmellow creme in a zip-top bag. Once you’ve filled the bag, squeeze out any excess air and then seal the top. Cut a small tip off of the corner to make a make-shift piping bag. Squeeze the creme into the bottom of the hole.