I think you're over thinking it a bit, the dev should have no problem getting it fairly close to how it looks from the gif as this is the exact same way I do things. If the end result isn't exactly what you envisioned it to be then sit down next to the "dev" or "John Doe" whatever you want to call him and tell him what isn't working and he should be able to fix it at a moments notice considering it isn't too far off from the original gif. I do this on a regular basis and it works seamlessly :)

Real talk though, who uses a trackpad? Lol