Change iTunes Store with card balance

RE: Can't change iTunes Store because of remaining store balance in previous store

I'm a teacher. My students are from Japan & South Korea. When attempting to change iCloud/ iTunes account info to local (Canadian) store, if there is a balance remaining in their iTunes Japan or Korea store, we cannot change store until the balance (in other currency) has been spent. But, the remaining balance is equivalent to less than one Canadian dollar (¥45)!! What can be done to override this requirement and 'forget' the balance?