skeltoac

You don't seem to prefer aerodynamic solutions but they are abundant so here's another one.

Orientation is unspecified so we can drop one object right-side-up and drop the other upside-down. A shape can be designed such that both orientations are stable (neither will switch orientations during free-fall) and such that one orientation has a different ballistic coefficient, creating a different terminal velocity. This could be accomplished with fan blades or pitot tubes of different sizes or protruding at different angles, converting different amounts of kinetic energy to heat depending on the direction of airflow.

Given only that both objects will splash into the Central Atlantic, there is wiggle room in choosing latitudes and longitudes such that lateral distance between the objects is vastly larger than the difference in altitude. Suppose the lower-altitude object is placed safely inside the eastern boundary of this region and the higher-altitude object is placed inside the western boundary, such that each will splash into the Central Atlantic according to the rules. The objects can be several 1000km apart but only 1cm different in altitude.

Now we just need a natural force to slow the descent of the lower-altitude object more than it slows the higher-altitude object. Let's use the gravity of the Moon. Drop the objects when the moon passes directly above the lower-altitude object. The Moon exerts a greater upward pull on the lower-altitude object, slowing its descent slightly more than it slows the descent of the higher-altitude object.