Quick and dirty way - Extract the files and run:
rundll32.exe setupapi,InstallHinfSection DefaultInstall 132 wvc1dmo.inf
I'd probably package the DLL into an MSI and deploy it that way.
Rundll32 doesn't seem to want to run unless the path to the INF is specified as ".\wvc1dmo.inf". Even then, the INF installer (invoked from the command-line or from right-click / Install) doesn't actually register the DLL! Here's a deployment script that can be placed into a share on a server comptuer and invoked as a startup script. (I think, for my networks, I'd still deploy this thing in an MSI, but I don't have time to build an MSI this morning).
rem Query for installation
reg query "HKCR\Software\Microsoft\Multimedia\Components\Installed\codec_wvc1dmo\Uninstall"> NUL 2>NUL
if errorlevel 1 goto do_install
rem Make temporary directory and copy down files
xcopy "%SRC%" "%DEST%" /y
rem Change directory and drive to destination location (as setupapi has to be called with
rem current directory .\ specified on command line. Dumb, dumb, dumb...)
rem Call setupapi to perform installation
start /wait rundll32.exe setupapi,InstallHinfSection DefaultInstall.Nt 132 .\wvc1dmo.inf
rem Dumb thing doesn't seem to register itself
regsvr32 /s %SystemRoot%\System32\wvc1dmod.dll
rem Remove temporary files
rmdir /s /q "%DEST%"
That works, and my conscience is somewhat clearer. Next time, I'll test a little more before I go posting an "answer". My apologies.