Well on a unix-like system I'd do something like
Elaborate on "more effort" on windows, evn? mklink /D <link> <target>.
That'll make the ~25 symlinks to the files/folders in the original warcraft directory in the new location. After that I can just replace the interface/wtf/fonts/etc folders in my new warcraft folder with whatever is unique to that installation. If I was concerned about being able to delete the original warcraft location or having full playable backups of each install I'd use hardlinks, but whatever.
ln -s /Applications/WoW/* -t .
On Windows I tried to do a similar setup. First I mklinked all the directories, then the files without the /d option. I'm sure there's probably some powershell equivalent to my 1-liner to make symlinks but I don't know much about Microsoft's new command line environment so I just made links one at a time to the 2 dozen files and folders that matter.
Then I replaced interface/wtf with regular directories so that they would have their own UI. Double click on wow.exe and I get "the specified path doesn't exist" as an error. See example (Windows 7 Ultimate 64-bit, updated, logged in as an administrative user). Symlinking folders on windows works as you'd expect. Symlinking files doesn't seem to.
I've read that explorer won't launch relative links but you can probably see in the terminal window that I created them with absolute paths so that doesn't explain why explorer is refusing to launch it. You can also see the absolute path to the target in the properties window and that the target file exists in the explorer window on the right. Strangely, the link will work if you try to run the executable from the command line (ie: in cmd.exe e:\w2\wow.exe works as advertised) so the links are sound, you can also see the icons are resolved correctly for the executable files. I recall needing some some third party software to make it work the way it does on a Mac where double-clicking the symlink is identical to double-clicking a copy of the executable - but I lost interest and can't remember details. Either way - it wasn't as simple as "type these 32 characters into terminal and you're done".
If you know something I'm missing then I'm willing to listen.