There is not much you can do. The main body parts and organs of guinea pigs are very fragile. You can do Heimlich Maneuver but it almost definitely will cause some damage to its internal organs, which can cause a whole another issue to deal with. So you really shouldn't squeeze or push them much. You can push his lungs as the vet doing in the video below but you have to be gentle. Just helping him a little more. http://www.youtube.com/watch?v=nmNl9X50jxk
Sorry you lost your pet. I expect he was a friend and you miss him. May I suggest you do to a pet store that sells Guinnea pigs and as for help with a sort if demonstration of what to do. You should have some idea of how much pressure to use when pushing wherever you should press in the event of a choking.