Spawning particles on a mesh

Essentially, all I want is to have my particle system(which emits small cubes upwards) spawn the particles from the top faces of my mesh. I'm trying to make a fire particle effect with cubes, due to the style of my game, so i need these to spawn on the top of the mesh, not around it, as it does with just the mesh shape applied to the particle system. Does anyone know how to do this?

Thanks, Etched