HLDS binds itself to 1 IP and only 1 IP. You can attempt to bind it to 0.0.0.0 and see if it will then accept traffic from both. If it doesn't, you can always try and use iptables to redirect the trafic, I've never done it with IPs before, just ports.
If this doesn't work, then you will need to accept that it is not possible
I do not browse the forums regularly anymore. If you need me for anything (asking questions or anything else), then PM me (be descriptive in your PM, message containing only a link to a thread will be ignored).