When an editor selects a component variant, make a "Choose audience" action available. The action should only be available when a component variant is selected. It should not be available when the component's original is selected.

When the editor executes the Choose audience action, open the standard Choose audience dialog. The editor gives the audience a name and picks a segment or traits, then saves her changes. The chosen audience is now assigned to the variant and the audience name is displayed in the variants dropdown, for example "Facebook visitor".