Add the ability to set an alternate relay address

Our situation :
We have 3 offices in Canada (HQ, A, B)
HQ-A have MPLS link between them,
HQ-B use VPN over internet.
All location have independent internet access.

We use access session on all system in all location, but the relay is located in the HQ.

Curent setup.
1 DNS name to the server that resolve to an external IP when out of the local infrastructure and an internal IP when inside the infrastructure.
- This way system on our internal network dont use the public internet access, it more secure, reduce the global bandwitch and load on our front end firewall.
The issue, if the inter-site link go down, the access session will not be able to connect, as the DNS will still resolve to the internal IP, resulting in disconnection.

Our need, be able to setup 2 URL for the a access session, as such when the 1st is irresponsible the client can try connecting to the second one, with a retest every X to go back to primary.
With this we could setup our client with a internal URL as primary and an external URL as secondary and still reach our system if the VPN or MPLS go down, but not the internet.