I remember hearing that it did in a thread a while back - any truth to this? I’d conduct an experiment myself, but i’m wearing new shoes.
Extending the tongue forward helps to supress the gag reflex. I have no info on smiling to keep from gagging. Maybe that’s like laughing to keep from crying. 
Anyone else know? I remember the poster said that was why a boxer smiled when they were doing something to him that caused gagging (no sex jokes).
I’m just giving this thread a bump because I was wondering if anyone might be able to answer this question now. I e-mailed samclem and he said it wasn’t a problem if I wanted to see if anyone could shed some light on the question.
I also remember reading a while back that rubbing your temples helps to suppress the reflex for a while, it seems to work pretty well for me brushing my teeth when I try to clean the back of my tongue.
This was mentioned in an episode of CSI. Sarah has a thing with saliva, and she was holding a spit bucket and grinning widely at Nick, who asked her what the hell she was doing.
I’ve done it to some effect since, but whether it suppresses the gag reflex or just distracts my mind (because I invariably think of that episode instead of what is making my tummy go whoopsy) I don’t know.
I also heard that rubbing the temples helps to suppress the gag reflex. Now, from my own unscientific exploration of the topic, it seems to work, but I can’t possibly explain why it would work, so I leave it to the Dopers to post their own results.