I should answer my own questions 
It is a good option and works by manually entering it in the options dialog (Add)
intf2d_enable_mi_read
yes
Once you set this, MI files was seen in the open dialog when set to all files or Creo elements direct (*.MI) files. No reason to reboot Creo.
It is by no means a transparent copy, but does open the relevant geometry correctly along with recognizable annotation.
Thanks again, Ronan!