There’s a way, it’s a bit hacky though.
What happens with Jets Afterburner mode is that it generates a wrapper Jets application and then proxies requests from the Jets app to the Rails app. This was a design choice.
As a part of the Jets application generation process, it’ll merge in the files from the .jets folder. So you could create a .jets/app/jobs/hard_job.rb. Again, a little bit hacky. Haven’t tested in a while, but it should work.