At least in Icon, try "/mov EMOTE_THROWSNOWFLAKES" - it works for me.
If using the Icon Development version (explained here:
http://www.cohtitan.com/forum/index.php/topic,8967.0.html), you can also use "/seqbits EMOTE UNDERHANDTOSS FOUR"
Unfortunately, while "/mov INSTANT_SNOWSTORM" and "/seqbits OPENHOLIDAYGIFT SKYSUMMON" do show the animation for the snowstorm, the summoned object is not client-side, and would require a separate command to place the object.
Edit: Agh
- just saw you're looking for the snow
ball rather than snow
flake. Oh, well. Leaving this here in case someone looks for what I included above...