Something small I created in about 5 minutes: a plugin that will show a TextBox and TextButton when you select one or more ParticleEmitter objects. Enter a number and press the button and the plugin will :Emit(n) particles from the selected ParticleEmitter objects.
Preview of the interface:
Here is the link to the plugin:
http://www.roblox.com/ParticleEmitter-Emit-n-item?id=303835976