captive portal automatic pop up without wan interface

Im working on a captive portal project for distribute application on my local area and one of the good feature of captive portals are that IOS and Android can detect it and automatically launch browser to show my landing page.

The parameters of project is this

1. I'm using a python script and iptables for as my captive portal
2. after user connection it should launch browser (android/ios check some urls like google.com or apple.com and if it fails it knows about captiveportal and opens browser)
3. all http requests automatically redirect to my landing page serving with apache.

What we have now:

every thing is working as expected when we connect wan and start wireless access point and captive portal service there is no problem!

What is the problem?

we do now want to share internet only deliver content with wireless, currently we should connect the wan interface to adsl modem, if we don't attach the wan interface, android/ios do not automatically launch the browser and we should browse some page by hand to redirect to landing page

My suggestion

I was thinking about solving this problem my theory is if we config an virtual wan interface and simulate google.com and apple.com to response with that virtual wan and reject them with iptables we can automatically open the browser! but its just the theory and i don't know how I can do it!! i fount some packages like http://ift.tt/1k7E2qj but its an appliance i need to implement it in a linux box with the captiveportal

I appreciate it if there is any idea for resolving this :)