Personally I would just throw a script for this service as you have described.

Commercially I would do my best to implement this using systemd features, then finally give up and throw a script but with extensive comments describing reasons why it has to be a script instead of a systemd unit file.

Well, my solution is a script and a systemd unit and timer files to run the script (the timer is just so that I can have it running 30 seconds after boot).