supplemental nudge

A light-to-moderate "assistance-push" that you give someone (or something that he's presently attempting to move) to enable him to more-easily complete some action or task that he's currently engaged in.

Two of my buddies had stopped to give me a ride in their pickup truck, and the passenger had scooched over towards the driver as far as he could; the problem was that because of the gearshift and large transmission-hump, he was unable to brace his feet against the floor in front of him to maneuver himself over sufficiently to make enough room on the seat for me; I therefore gave him a supplemental nudge with my hip to slide him over the rest of the way so that I could plop down and shut the door.