Just go through the reservation page and it will tell you the cancellation charge. But I would strongly advise against this as this could be considered as fraud. Also per the condition of carriage, JAL has the right to refuse the refund
http://www.jal.co.jp/en/carriage/index_c012.html
JAL may refuse a refund for a Ticket which a Passenger presents to JAL or to government officials of a country as evidence of his/her intention to depart therefrom, unless the Passenger establishes to JAL's satisfaction that he/she has permission to remain in the country or that he/she will depart therefrom by other Carrier or other transportation service.