pt-online-schema-change - make stoppable and restartable

pt-online-schema-change is a great tool. For some large tables it can take a long time to run and sometimes for a number of reasons you may need or want to stop the script but be able to later continue at the same point in time. Given the way the script already knows where it is in terms of copying chunks of data over, it would be great if you could interrupt it and make it save its state so that the script can be restarted.
My issue: I forgot to run this on a job that was scheduled to run for 48 hours under screen and realised after running it for 8 hours.
I'd have loved to have been able to do ctrl-C, enter screen and then do something like pt-online-schema-change --continue.
If the triggers are not touched this shouldn't cause any issues. You could even move the server/host you are running pt-online-schema-change on if you also move whatever file(?) is used to store the state.