Sadly, that particular npc was actually from the original version of FFXIV (1.0) where he had the exact same costume, so I assume it was specially made for that npc (his name was Percivans in case you were wondering). Unfortunately, cowls specifically are designed to replace the head slot - specifically you cannot equip anything into the head slot while a cowl is equipped, which is probably for clipping reasons - too much headgear would clip badly through it and just look stupid.

Of course things like headbands and facemasks would work, but as that would require those kinds of items to be separated from other types of headgear, I don't see SE doing something like this to be honest I'm afraid.