Machines from this company are easy to find at ICN. You stick in a credit card, show it a passport, it produces cash.
https://www.wowexchange.net
You can decide for yourself if you think the exchange rate is worthwhile.
Once he has cash he can put some of it into a TMoney card (you need some cash to initially buy a TMoney card - about 4,0000 - but it can then be topped up by bank card - note that a TMoney card is going to be way more useful in Seoul than the boonies)