Just wanted to stress that this is a very real risk. Gulf Air has one daily flight out of BKK, either 151 or 153 to Bahrain depending on the day of the week. They will not have spare aircraft sitting around in case one breaks, or a whole lot of spare parts in case something major needs fixing. Since you are not especially interested in seeing Bahrain or, as far as they are concerned, London, and there are lots of other ways to get to the States, the two of you are prime candidates for being sent to your official destination another way. Saying "we really don't want to go to the States, but a round trip was the cheapest way to get to London" won't cut much ice.