Thanks @Brian Sorensen 

That's really useful. We haven't moved our RITM's to flow's yet (still workflows), but I have used your syntax of ${document_id.variables.variablename} in the notification and it works perfectly. 

So you use the standard Variable Set across all the RITM's and differentiate them by Item Name and Business Reason? Presumably any other variable on the RITM's aren't used for approval and are only of use to fulfillers inside SN?

Thanks again

Steve