Installing the IE8 Administration Kit should install the IE8 version of the file you want (inetres.adm) -- or you can grab the file from any machine that has IE8 installed I believe (the file should be identical across platforms -- grab it off your home machine). Copy the file into %windir%/inf/.
Free bonus: The settings that should be exposed.
This guy seems to have made a cute little installer that installs the same inetres.adm file that my server has for IE8 (based on MD5 check). He also has the ADM file available, which you could open in NOTEPAD/Wordpad/Your favorite text editor to confirm its nothing malicious. YourMilageMayVary on this one.
I get the feeling that installing IE8 on the DC would do what I need
Correct -- that would also install the inetres.adm for IE8.