Stick your finger down your throat without gagging
If you hold up your left hand and squeeze all your fingers as tight as possible, squeezing down your thumb you can stop the gagging reflex when putting your finger down your throat.
I know some of you may think this is a trick which is fair enough. But I just read it online and it worked for me. It's something to do with occupying the right hemisphere of your brain (which controls the gagging reflex as well).