msiexec /quiet /i My.msi WEBDIR="C:Path1" /l*v InstallationLog.log

<Property Id="WEBDIR">
    <IniFileSearch Id="WebsitesDirIni" Name="MySetup.ini" Section="InstallLocations" Key="WebsitesDir" Type="raw"/>
</Property>

<Directory Id="TARGETDIR" Name="SourceDir">
    <Directory Id="WEBDIR" Name="Path3">
    </Directory>
</Directory>