I currently extrude a sketch up to a surface with the FeatureManager.FeatureExtrusion2 function (C#):

     feature = ((Feature)(SWDoc.FeatureManager.FeatureExtrusion2(true,false,false,4,0,1,1,false,false,false,false,0.1,0.1,false,false,false,false,false,true,true,0,0,false)));

Is there a way to extrude a sketch up to a surface with IModeler interface to create a temporary body?