Hi Mohammed,
This is a piece of functionality we are looking to add in either a sample or in the api directly in the near future. In the mean time this can be a complicated task to solve that would require modification of the SDK code. The ArcGISTerrainOcclusion is doing this but only for Integrated mesh layers, this could potentially be ported to work with regular GO's but I cannot recommend doing that at this time because I know it would be a lot of work.