For starters, you couldn't use our canned gesture classes. The way you could do it would be to check various conditions of the hand periodically. For the stop gesture, these conditions could be:
- 5 fingers extended
- Hand direction within a certain number of degrees from horizontal (i.e. fingers pointing more or less up)
- Palm normal within a certain number of degrees from forward
- Hand velocity less than a certain value
You will have to experiment here.