To retrieve a guest portal's URL to be statically configured on a NAD for LWA scenarios, with ISE 2.x we can use the "Portal test URL" option under the portal's configuration page, pointing to something like
https://<ISE_IP>:8443/portal/PortalSetup.action?portal=a23a3c92-fd52-11e6-9a8d-0050568c1f41
This would be used to statically point your WLC to the ISE PN
