Is there a way to use the hostname for captive portal instead of IP?

Really, the subject says it all... is there a way to configure the HTTPS & HTTP proxies to redirect to a hostname instead of the IP address of the firewall?

Reason I ask is I'd really like to keep my certificates consistent.  We use an internal PKI, and so I have issued the XG a valid certificate based on our root cert.  Yes, I can go back and re-issue it with the IP address, but I would like for it to redirect, if possible, to the internal hostname instead.

Similar to overriding the hostname for the external SSL vpn... I want to do it on an internal-facing service.

If the answer is currently "not possible" - I would like to suggest this as a feature.