Plenty of inventive (and desperate) people have come up with a number of imaginative schemes for sneaking themselves and others across national borders.
On 2003, Illegal immigrants from India and Pakistan being smuggled from mainland China to Hong Kong were found inside suitcases).
On 2001, a 135-lb. woman was hidden behind the dashboard of a car. The "passenger" might be quite cramped and uncomfortable and the automobile difficult to maneuver after the modifications, but the ruse wouldn't have to be maintained for long — the car could be loaded just out of sight of border agents, driven the short distance to the crossing, and unloaded not far across the other side.
Similarly, another would-be border crosser was caught attempting to enter the U.S. concealed inside a seat occupied by another passenger: