Just stumble into this thread

Actually my goal is to play (downloaded) video in mkv format so I don't have to convert it in order to be recognized by my Head Unit. But in the end, my Head Unit can play mkv file, view office docs, play game and has a customizable menu.
Here what I do :
I'm using Chinese Head Unit which the GPS files are inside an SD card. Just try to remove your SD card safely and copy to a folder (let's say SDbackup) in your PC/laptop. Inside this folder, you will find *.ini file which specify the path to your GPS problem. Open this file. Mine (maplaunch.ini) is look like this :
[igo]
path= mobilenavigator\mobilenavigator.exe;
iconpath= mobilenavigator\igo8.ico;
showname= igo8;
Then search for a PORTABLE (no-need-to-install) shell menu or application launcher, I use GPS Menu. Copy that portable launcher/shell to your SDbackup folder while keeping the folder stucture the same. I have no info about this chine head unit, Therefore I use portable launcher so I dont have to install and taking chance to brick it.
Then edit the executable path in *.ini file above to point at the portable launcher *.exe. (Mine become path= my_gps_menu\gps_menu.exe

. I cand do this since the wince only lock the IGO map folder. If it's also lock the path above , then copy the portable launcher files into the folder path (ie mobilenavigator) and rename the gps_menu.exe to mobilenavigator.exe.
Copy the SDbackup folder to a new SD card. Keep your original GPS's SD card as a backup.
Try this new SD card on your head unit. If it's boot up perfectly, then you can edit this launcher to display your existing GPS apps and other apps. "GPS menu" has include some apps like tcpmp video player -which can play mkv & subtitles, music player, document viewer, game etc.(I guess the last two just for showoff

). You can also 'unlock' (accessing the wince desktop) the Head Unit,
Good Luck! and Sorry for my english.