How to add a scene to my renderer that is not affected by my EffectComposer ?

Hello,

I'm using the EffectComposy to create a mask on my renderer. It works fine : I have my mask and into it a scene.
Basically I would like to have another scene as a background for my canvas but my new scene doesn't appear and I think it's because I call my whole renderer like this :

`var composer = new THREE.EffectComposer(renderer, ...`

Do you know what can I do ?
Thank you very much, I think I want to avoid creating a new renderer.