The pilot, and two passengers, were taxiing for takeoff in a wheel/ski equipped, tailwheel airplane. The flight was a VFR air taxi flight from a remote lake. The landing/departure area was about 3,500 feet long, and covered by soft snow. As the pilot began to taxi, he noticed the snow was softer than anticipated, so he began several taxi runs to pack down the snow for takeoff. During a turn, the right ski encountered soft snow and sank. The right wing struck the snow, and the airplane nosed over. The airplane received damage to the right wing, and propeller.