How do I set up custom shader options without killing batching?

I read this article recently and it made me curious to see if I could write my own stateless particle system.

http://www.gamasutra.com/view/feature/130535/building_a_millionparticle_system.php?print=1

I thought I could do this with the help of a vertex shader to modify the vertices of the particles. However, I'm not sure how I should set up taking the initial parameters for the shader. The equations within the shader should be simple enough, but I'm stumped for how to get the initial values (like velocity). If I make the initial values properties of the shader, then I'd need a different material for each representation of those values, regardless of the fact that they'd all share a texture, right?

If anyone knows how to set up a shader so that you can put some initial values into it per object without messing with the materials, I'd be glad to hear it!

P.S. I'm still fumbling my way around shaders, despite having written a few. Please excuse me if my terminology is a bit off and feel free to ask for clarification if the question isn't clear!