Stoss qualified for the men's 200 m backstroke at the 2008 Summer Olympics in Beijing, by eclipsing a FINA A-standard entry time of 1:59.27 from the European Swimming Championships in Eindhoven, Netherlands. He challenged seven other swimmers on the fourth heat, including three-time Olympians Răzvan Florea of Romania, Simon Dufour of France, and his teammate and two-time Olympic silver medalist Markus Rogan. He raced to fifth place and nineteenth overall by fifteen hundredths of a second (0.15) ahead of Japan's Takashi Nakano with a time of 1:59.44. Stoss also tied his overall position with Hungary's Roland Rudolf.