There's a way to scatter points based on a geometries animated path but I've completely forgotten how. I seem to remember it's simple. The trail node seems to be what I'm looking for but I can't think what the expression must be to get it to work how I want.
edit; um, I just had to input the number of frames I wanted into the trail parameter trail length. Forgive me. I panicked as I was sure it was an expression. Or is it this way... I'm sure there's a better way.