Can't help you with the NAS file. However, if you know when your ancestor was removed and which Poor Law Union (PLU) in Ireland he was sent to, it can be worth looking up the Board of Guardians minutes in Ireland. (In PRONI, Belfast for Northern Ireland). Their records are pretty complete.
I have seen several where individual cases were referred to, and where they authorities in Ireland were a bit skeptical about the decision to remove the person back there. The legislation appears to have said that the destitute person could be sent back to the previous parish/PLU that they resided in, but not if they had been in the current one for 5 years or more. The 5-year rule, plus the fact that the person may also have lived in several other places in Scotland since leaving Ireland which meant they should have gone there rather than Ireland, was reportedly often “overlooked”, and they were just sent back to Ireland anyway, and with no means of making their way from the port to their original PLU which might be 150 miles away. So the Boards in Ireland often felt the person shouldn’t have been returned to Ireland at all, nor should they have been left destitute at the docks.