Nope.
There's this:
If PortalSettings.ActiveTab.ParentId = PortalSettings.SuperTabId Then
rowType.Visible = True
optType.SelectedValue = "P"
Else
rowType.Visible = False
strMessage = String.Format(Localization.GetString("DemoMessage", Me.LocalResourceFile), Convert.ToString(IIf(Convert.ToString(Common.Globals.HostSettings("DemoPeriod")) <> "", " for " & Convert.ToString(Common.Globals.HostSettings("DemoPeriod")) & " days", "")), GetDomainName(Request))
lblInstructions.Text = strMessage
btnCustomizeHomeDir.Visible = False
End If
This means that whether or not the current user is superuser, the anonymous demo creator can specify a parent portal and home directory simply because the parent of the active tab is the host tab.
When specifying a tabid that isn't under SuperTabId, (like my home page /tabid/36/) I get a page with no modules injected.
So, I'm unable to reproduce the behavior seen here: http://demo.dotnetnuke.com/tabid/36/ctl/Signup/Default.aspx .
So, the choices are currently to use the URL of the host's Add Portal page, which will allow the user to create a parent portal that won't work until someone sets up IIS and DNS and allows them to specify the directory name; or, a blank page.
The only way I've been able to duplicate the functionality of demo.dotnetnuke.com is to create a module from signup.ascx and put it on another tab.
If' there's no magic, then what's causing the blank pages?