This looks like it might be relevant - but it involves scripting (which I'm not confident with yet): https://netsuite.custhelp.com/app/answers/detail/a_id/26158/kw/upload%20file%20attachments Does anyone know of any other ways?

Thanks Dominic - that's really useful. It's a worry that the NetSuite consultants can't give us these options! I will try that on the next data import and see if that improves things.