So far so good. I now have a one line command that performs all the system assigns to a path you define:
i.e. SysDisk DH0:OS/3.9 will perform the equivalent of
Assign Sys: DH0:OS/3.9 Path
Assign S: Sys:S Defer
Assign L: Sys:L Defer
Assign C: Sys:C Defer
Assign Devs: Sys:Devs Defer
Assign Libs: Sys:Libs Defer
Assign Fonts: Sys:Fonts Defer
Optionally it will also do things like HELP, LOCALE, and add CLASSES to Libs:, etc... if you supply the WB or WORKBENCH parameter to the command.
I have a little bit more debugging and source cleanup to perform and then I'll post it on aminet. If anybody has an interest or feature request please let me know.