If your friend is a Uk resident, there's a few online companies that do these type claims for less than 100 pounds... if your friend is planning to come back to uk for at leat 1 month, you could file a small claims...
knowing SQ, they will produce that document, saying they have tried to accomodate the request out of goodwill, saying they are not obliged to as they are not a Uk carrier and so forth..... the court will charge interest rate payable by SQ UK.... it just depends on how long you wish to drag it for.... If your friend has no intention to take sq anytime soon and there is no other anxillary issues such as medical claims, that will be ok...just take the money. the waiver was simply stipulated by the SIN office and most of the time, the default answer to the customer is always no.