There are several methods which might work with some experimentation. Particle Playground in the Pro version allows you to control a stream of characters.
Third party effects like Trapcode’s Particular can use any source as a particle.
The Foam effect can use a layer as a particle but you need to control the region the particle occupy using a Flow Map and the particle orientation needs to be controlled by its velocity. In addition each instance of the particle is identical so you may need several layers with the effect applied to achieve the desired result. Foam is applied to Solid layers and uses other Comp layers as a source for the Rendered particle. Set the wobble ammount to 0 otherwise the letters will change shape (may that would be cool.)