I messed with forcing cad to use the current folder as the starting place for the xattach command. Below is the key I found, and this key updates as you use the command.
'HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R16.2\ACAD-4001:409\Profiles\<<Unnamed Profile>>\Dialogs\XattachFileDialog
With a registry module from the old Cadvault I can successfully change this key, but unfortunately it doesn't work, has anyone figured out how to do this?