You can have whatever you like, but it comes at a price and that is where it doesn’t always make sense for the civil market to follow the military.
I should imagine the mounting of external aux tanks on the S-92 is pretty straightforward. However, I suspect the costs and penalties associated with not only beefing-up the sponsons and cabin structure, but LCF penalties to the dynamic components as a result of increased external load that far out and drag would result in a substantial rise in DOC’s and that I suspect is the reason for the civil S-92 having internal aux tanks.