* Nikkei adds 0.4 to finish just below 9,600 * Elpida jumps after GS, C.Suisse lift stakes * Mazda sheds 6.8 pct on 162 bln yen share offering plans By Dominic Lau and Mari Saito TOKYO, Feb 23 (Reuters) - Japan's Nikkei share average rose on Thursday to end just below 9,600, underpinned by a softer yen which boosted risk appetite, as it headed towards its best February performance in two decades. Buoyed by a run of strong U.S. economic data, the European Central Bank's liq