After editing services_captiveportal.php  exclude the bridge check 

/* make sure no interfaces are bridged

                for ($i = 1; isset($config['interfaces']['opt' . $i]); $i++)
{

                        $coptif = &$config['interfaces']['opt' . $i];

                        if (isset($coptif['enable']) && $coptif['bridge']) {

                                $input_errors[] = "The captive portal cannot
be used when one or more interfaces are bridged."

                                break;

                        }

                } */

It worked fine. No need to do any thing else - unlike I though in the
beginning.

I tested it with VLANs I did not have physical NICs to test that but it will
same. 

After enable opt1 and select bridge with LAN then reboot , 

After reboot I went to interfaces assign page, found new + clicked on it 

Gave me bridge0 (02:8c:c8:bd:71:16) as an interface 
So I went to captive portal simply found it out there 
Choose it and it worked perfect
 
I guess making sure no interfaces are bridged need to get tuned to know the
difference between bridged interfaces - bridge members - and the bridge0
interface.
 
Regards, 
Mohammed.