Here's the realisation of the idea I mentioned yesterday. The hand animated portion of this is quite small (14 frames) but the processed output is extremely long (840 frames). I could add more bouncing balls but the length/size of the output blows up quite fast.
I was actually mistaken, Aseprite does have a scriping facility which allowed me to accomplish this without writing a seperate program (what threw me off is that it's a recent feature which I needed to update to get, and it has an unrelated "extensions" feature which is not useful to me). The scripting is in Lua which I'm quite familiar with so it wasn't too hard to get this going.