[roman]

Ok. Pero ¿no puede hacerse así?

TDBLookupControl = class(TCustomIncSearchEdit)
  procedure UpdateDateFields; virtual; abstract;
  procedure UpdateListFields; virtual; abstract;
  procedure ListLinkDataChanged; virtual; abstract;
end;

Un DataLink:

TListSourceLookupLink = class(TDataLink)
  private
    Lookup: TDBLookupControl;
  protected
    procedure ActiveChanged; override;
    procedure DataSetChanged; override;
    procedure LayoutChanged; override;
    ...
  public
    constructor Create(ALookupInterface: IDBLookupControl);
    ...
  end;

implementation

{ La misma, cambiando ILookup por Lookup }

Uno de los componentes:

  TCustomDBLookupControl = class(TDBLookupControl)
  protected
    ...
    procedure UpdateDataFields; override;
    procedure UpdateListFields; override;
    procedure ListLinkDataChanged; virtual; abstract;
    ...
  end;

// Saludos