This may sound strange but I have tried this on several people and it works most of the time. If you know someone who has the hiccups you have to distract their mind from that fact that it is actually happening. They key is to figure out a simple question to ask them but the answer is somewhat elusive or may take more than a minute or two to think of the answer. Basically you want them to "rack their brain" over a question that seems so simple.
For example you notice someone you know or dont know with the hiccups, approach them and say you may be able to help with their hiccups. When they agree ask them "What did you have for supper last thursday?" or something to that effect, so that they can eventually get the answer. (As long as the person thinks for an extra few minutes or so it may be just long enough to make the hiccups disappear.) Then, once the person has finally got the answer, pause and see if the hiccups are gone, and I would say about 6 to 7 times out of ten they are gone. Then, ask "How are the hiccups?" If you asked the right question and made them think long enough, they are surprised that they no longer have the hiccups. Its totally a mind over matter situation. Its fun trying anyways. You can apply the same principle to yourself, only the question may be a little trickier.