The current situation seems to be this:
You are licensed to use the plug-in on a Mac or a Windows PC if you have purchased and installed H5-VS software. Since H5-VS is only a Windows product the download for the plug-in is a Windows EXE because when you run that EXE it'll check for the H5-VS software installation and if it doesn't see it, it'll stop, so to be successful in extracting the Mac plug-in you have to use a Windows PC.
You can examine the contents of the LRPLUG.EXE by renaming it to something like LRPLUGIN.EXE.ZIP and opening it with 7ZIP; however, the contents aren't something where you can just extract and run w/o the license check.
The only way forward seems to be to purchase the H5-VS software and install it on Windows and then download and run the LRPLUG.EXE on that same Windows computer to extract the plug-in installers, and then run those on the appropriate platform.
However, the H5-VS software doesn't appear to be for sale, anywhere, although the Fuji people do seem to hint they will have a solution at some point in the near future--perhaps it is only available in Japan ATM.
Most of this information was gleaned from the download page for the plugin, here:
Which is the page you get to after agreeing to the terms and conditions of downloading the plug-in from this page:
The bottom line is that while the tethering plug-in is for both a PC and a Mac the licensing dependency is on a Windows-only program so the initial plug-in installer is a Windows-only program and the missing link is how to acquire the required H5-VS Windows program to satisfy the licensing requirement for the plug-in.