An apparatus is provided for applying an adjunct element to at least one of opposing first and second jaws of an end effector of a surgical stapler, wherein each of the first and second jaws includes a stapling surface and an external surface opposed from the respective stapling surface. The apparatus comprises: (a) a platform configured to be positioned between the first and second jaws of the end effector; (b) an adjunct element positioned on the platform; and (c) at least one closure surface opposed from the platform, wherein the at least one closure surface is configured to mechanically engage the external surface of at least one of the first or second jaws to thereby transition the end effector from an open state toward a closed state for placing the respective stapling surface of the at least one of the first or second jaws in contact with the adjunct element.