Thanks, I figured it out too meanwhile! I just also completly forgot I posted this thread!
However, it doesn’t work with all meshes shapes unfortunately 
I didn’t had the time to do some testing, but I think the meshes needs to be closed, like simple collisions (for example, walls made with planes can’t be used as collision if copied from another static mesh).
it would be nice to be able to use another static mesh as complex collision!
I put it as resolved, even if it’s half resolved, as it might help other people!