This post mentions that it’s being worked on: New Logging Infrastructure - #5 by steve
One hacky way to do this now (as I’ve done on other providers like Digital Ocean) is to run a Docker image with multi-process support. In there you would run fly log and send its output to a file, while another service like Vector may consume it and ship your logs off. Here’s an example of that from LogDNA.
I just got started with Fly, but I’ll give this a try and see if it works there.