Start at the Schreckhorn hut like for the regular route. Go done to the glacier using the clearly marked path and hike up the glacier until you reach the former place of the hut. From there a path leads up using a gully called "Gaag". Very rotten, a real bad thing by night with head lights.
If you reach the top of the "Gaag" the route leads on snow to the glacier basin at the base of the Schreckhorn S-face. From there the S-buttress is visible at the right border of the S-face. Up to this point it's the same route as the regular route, most time there will be a good trace.
Climb the bergschrund (may tricky some times) and reach the base of the butress. On good conditions leave crampons and ixe axe there.
It may take about 3-4 hours to reach the base of the climb.
The first pitches going up on the left side of the butress wich is not very prominent at the beginning. Climb up searching the best way as you like it. Little danger of rock fall. The routes leads close to the prominent ice gully right of the S-butress to a corner. After this corner the climbing gets steeper and more obvious.
Cracks leading to the crux : two pitches of a very steep crack, sometimes icy (5/5+). Those two pitches can be avoided using a chimney somewhat more right (still 4+/5-), using the cracks is the better choice.
Above that the route follows the meanwhile prominent buttress : a steep, difficult but short passage (5-) leads to a pedestal. From there the crest of the butress leads to the summit ridge. Following this brings you to the summit (4).
It may take about 4-5 hours from the base of the climb to the summit.
Descent the regular route, it will take about 4-5 hours to the hut. Do not underestimate this descent, it's a long way down and the area doesn't allow any errors.
Crampons, ice axe, ice screws, rope
There are no bolts at all, so bring friends (up to 3), nuts, rocks and slings. Some pitons may be usefull in case of trouble / drawback.
The route gets dry after bad weather very soon.
Do not use the gully right of the buttress for ascending, this is (a) an other route and (b) dangerous because of rock and ice fall.