How do you handle group changes and solved tickets?

If you have agents who sometimes switch groups, you will run into a problem. When an agent is removed from a group, all tickets, even *solved* tickets, assigned to them under that group, immediately move and assign to the oldest group member instead. This then throws off all kinds of reporting on who solved issues. I want solved issues to update to the default group, same assignee,  so that the agent who worked them still gets credit for them. 

I was given a trigger path to try by Support, but it doesn't work for me, because we often have automations solve out tickets, and the trigger would require the last person to touch the ticket, to be the agent.  It also appears that this kind of ticket move does not trigger the addition of tags added to a user, so that doesn't work to try and set up a way to push them back to the right assignee, either. 

Does anyone have any suggested workflows for this? Doing it by hand is just not working, sometimes it's a thousand or more tickets and I cannot do this manually. This is also why automations are not a good option -- this task cannot take multiple hours to complete before I am allowed to update their groups, and automations can only do 1k tickets an hour, plus you have to wait for them to run. 

At this point, I'm going to try writing up a method via the API as I'm not seeing any alternatives, but if anyone has one that doesn't require the API, I'd love to hear it.