Thanks Kremmen that's also a great tip.
I sorta hacked that, by using 20 pin headers in the schematic (and created all the modules in the one schematic.)
I then separated them out enough so the Rat lines only wanted to route via those connectors.
Then when it came to the PCB's I created a new file for each module, attached the schematic and deleted the groups of components etc I did not want.
This way when I updated the schematic, the components I had laid out on the PCB would update(ie change components and/or numbering etc) and it would import the "unused" ones to the side, making them pretty easy to delete again.
Plus it allows me to colour code Nets all the way through the layout makining it much easier to follow.
So it certainly works or my limited requirements, and is not that cumbersome either.
Really happy with the way Diptrace works, I doubt I will be returning to Eagle (except to import/export)
Thanks for everyone's help!
CHeers Ben