Hello, I was already build in the past, custom entries using only "regedit /s" with "uninstall" registry entries...
Curiously I try to create using only "uninstall" registries, and was failed (no display in Add/Remove...)
The workaround was to use a sample "MSI" Package using wise MSI Editor 6.0 (the one will not any more delivered with DS 7.x 
)
With a unique "setup.ico" file to display a smart icon in the add/Remove list, and the "Add/Remove" settings.
(Why do I do that? Just for simplifying the Software inventory and licence management... Just ask me if you want more explain ;-)
But I wonder your own experience regarding such ?
What I see is a few more registries done from Wise Editor: (I investigate using SWV 6, alias SVS)
And I see a similar "uninstall", additionnal "InstallProperties" in a "localSystem" HKLM entry:
- HKLM/Microsoft/CurrentVersion/Installer/Userdata/S-1-5-18/Products/
And I see 3 GUIDs:
- Features/Products,
- UpgradeCodes,
- Uninstall MSI GUID code (the one registred into MSI package)
Hum... I will keep the MSI editor workaround, but I still wonder if we can just create "fake" Add/remove entries using a simple REG file ???
Did you ever build such ? And can you share with us your own REGISTRY file template ?