You'll need to edit the raw MSI file. You can do that with Orca (install from
Orca.msi from the Windows Installer section of the Platform SDK). Open the MSI
file with Orca, go to the Property table in the left hand pane. Change the Value
of FolderForm_AllUsers from ME to ALL.
You could automate this if it gets tedious. VBScript can open and edit the MSI
file with the Windows Installer automation object.