I would say the main issues will be security, i.e. locking down SQL server (and the Recorder database within it) such that only the authorised users can log in. I'm not an expert on SQL Server, so I can not talk about specifics. In the PostgreSQL DB server , one can limit access to individual databases based on user and network address and the type of authentication protocol (SSL, MD5 etc).
What type of WAN is it? This may influence the solution. There are going to be issues surrounding the network interface to the WAN, routing and firewalling etc.
As far as Recorder goes, it should be possible if it's a true client-server system, i.e. the front end talks to the DB server only via the network and does not reference any LAN resources. If it does only use the network (I can't look at the Windows registery to check up on something at the moment as we have gone back to Recorder 2002 until the next Rec 6 upgrade is out) then all should be well.
When I installed Rec6 workstation, I did so from the LAN. I note that on the Rec6 install disk in the system directory is the workstationsetup.exe file. So, it should then be possible to try and install that on the remote client machine and test if the installer can "see" Recorder server once that has been exposed to the WAN. Your remote workstations will need a network path to your SQL server.
Sorry I can't be more specific - I'd be really interested to see if this works. Not knowing the pre-conditions of the Recorder workstation installer (one for John maybe) I'd have thought it's possible, provided the client app is happy to operate purely over a TCP/IP network.
There are quite a few inter-dependent variables in all of this, but my thoughts to you would be;
a) Get the network side configured first such that, at least, the remote stations can "ping" your server.
b) Expose Recorder to the network within a security policy.
c) Then try and install Recorder workstation on the remote machine.
Brave new world me thinks!