Offline Captive Portal on OpenWRT

An OpenWRT router (LinkIt Smart 7688 hardware) is used for creating an offline hotspot. The hotspot doesn't have an Internet connection. I want to configure captive portal on the router such that any user who connects to the hotspot is automatically redirected to the web page hosted on the same router. No authentication required - just a redirection when the user connects to the wifi. The preferred approach is to use NoDogSplash with a made-up static WAN IP address. I expect a script which will add the functionality to the router.