Get yourself a domain name with a service that provides DDNS. You will point some A record to your dynamic entry, such ad home.mydomain.com.
At home, set up a DNS server with a similar A record, but this one points to your server's LAN address.
Configure all your systems to connect to that FQDN. When you are away, external DNS servers will yield your dynamic WAN address. When you are home, your DNS servers provide a LAN address.
You'll need to configure your firewall to port forward to you server.
You don't need a local DNS server, you can do it with your hosts file. Or, get a real gateway that can do full NAT Port Forwarding, which is what I do. But, otherwise, yes. I don't use access keys at all, because I have a dyn account and a decent gateway.
But that mostly addresses access from outside the LAN, which wasn't the original question.
If you have an always on server on your LAN, it probably makes sense to assign it a static IP address on your LAN. With a typical consumer router, if you do want external access at all, you'll
have to anyway in order to set up the port forwarding. But it isn't hard to do. It'll take seconds for most people to accomplish, if you only have one server. The clients, of course, don't need static addresses, just the server.
So,
the simplest solution is to just set up two entries in Gizmo, JRemote, MC's Library Manager, or whatever. One, that you typically use, with the Access Key, and a backup with the static internal IP of your server. That won't save you for
external access if something bad happens to connectivity, but you could always get to it locally if needed.
Any alternative for external access to this that is practical with a typical home DHCP assigned WAN address internet connection, will
require a service like dyn or noip (which, by the way, just transfers he "downtime" risk to a different company). JRiver's Access Key system
is a kind of dynamic IP resolving system, it just doesn't use DNS, and has some special sauce to eliminate the need to set up Full NAT firewall rules (or use hosts file trickery).
But let's be frank, if you do lose access to your Access Key, it is probably far more likely to be due to an outage at your house (on a residential Internet connection) than JRiver being down. That did just happen of course, so the memory is fresh. But you all never noticed this before because it is pretty rare.
If your home connection is down, then no amount of dynamic DNS trickery would have saved you for external access because
your Internet is down. That's why I'd say the simplest solution is to just add that backup version for LAN use (if you can't remember the address and port number to enter it then, should it ever happen).
The biggest problem would be if you're using multiple servers. I imagine the most common use case would be for remote control over a variety of HTPC's in a house (in addition to a main Library Server, I suppose). If you have this kind of setup, and especially if Gizmo or JRemote are the
sole controllers for the systems, then I'd recommend a more advanced Network setup anyway, just to manage it, if for nothing else.