Populating InstallSource and InstallData

Hi all,
Iam trying to update the registry key under the following:

HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall

I want to add the registry key "InstallSource" which would be dynamic. The installsource could be from desktop or c:\ etc etc. How can I update the same?

Regards
Pradeep

WriteRegStr HKLM Software\Microsoft\etcetc InstallSource "$EXEDIR"