You can't remove a wall in CSS. Walls are loaded from the BSP file and are in the part of the BSP file that gets checked for consistency. You can add entities. What I was suggesting was to spawn a prop_dynamic or prop_physics, set it to a flat model (like a big board) and freeze it in place.
If you want it to be invisible, you'll have to set it's render property to something with a 0 for the alpha mask or create a see-through texture that and use that as the models texture when you create the model (using the Source SDK tools) that will be used by the plugin.