Use a env_render to render the func_illusionairy invisible. As for the clip brush, remove it and place a func_wall_toggle textured with the null texture. When you'll trigger the env_render the wall will disapear and in the same time trigger the func_wall_toggle to make it disapear.
If you want to make it reaptable, just trigger the func_wall_toggle and use my
technic to make rendering process repeatable. Instead of the two trigger_changetargets that in the example change the teleport's destenation use env_renders, one will render the object visible one invisible.