It can be done, just not with GSC. As you need to mess with the angles before they are sent to the server if I can recall correctly, anyway you have to edit your angles found in the usercmd_t struct like you would with silent aim so that you can still actually see what you are doing and you can't do that in GSC. If you tried just making something like that in GSC you wouldn't be able to control what you are looking at.
It can be done, just not with GSC. As you need to mess with the angles before they are sent to the server if I can recall correctly, anyway you have to edit your angles found in the usercmd_t struct like you would with silent aim so that you can still actually see what you are doing and you can't do that in GSC. If you tried just making something like that in GSC you wouldn't be able to control what you are looking at.