How to create two clients if using RedisStore?

I'm trying to implement redis pub/sub, and I want to use redis in order to store sessions. How can I create two clients for one store ? I found how to make one client for store:

app.use(express.session({
        secret: 'mysecret',
        store: new RedisStore({
            client:db,
            secret:config.db.auth
        })
    }));

But how can I make more than one ?