The only way to do this is via the Formativ Control Panel applet. Select the ‘User Interface’ tab, and select the applet to execute if no portals have been defined (you can also just supply the name of the applet without a path).
This action writes an encoded entry into the registry – see HKEY_CURRENT_USERSoftwareAdvansys Corporationformativ1.0Settings
Value: Portal Folder Default
You could have your installet write this value into the registry on setup.
I hope this helps.