No, it's not working! :-(

After spending some time on internet I also found that TARGETDIR cannot be changed using installer class.
http://www.dotnetmonster.com/Uwe/For...nstaller-Class

However, I succeeded to search for the registry value in Launch Conditions, so now plugin installer only launch if main product is installed.

But again even if I change TARGETDIR value of Application Folder, how can I stop installer asking for target directory? I want installer smart enough to find target directory without asking for the location.