The best known cure, in my opinion, for a side stitch, is to put your hand on your head, and blow all your air out. Once you have done this, blow even more air out . Then when you inhale, try to do it smoothly and slowly. This is more of a quick-fix than prevention, and it isnt perfect, but it could help if you are in trouble.

I'm not sure what speedwork you're doing, or how you determine your pace.  But slowing a little may help prevent the stitch from starting.  Another technique that may help keep it from starting (and works for me) is closely related to the tips above: belly breathing. Make sure to breathe with your belly, your diaphragm, not just with your chest/lungs. It may take some practice but it should help.

Len