What the the most realistic and practical ways for a PhD in physics who has left the fold to return to a career of research in physics? The traditional employer of choice, universities won't hire such people. What alternative career choices are there for someone without an impressive track record so far? Are there alternative forms of support, or part time careers earning just enough money to get by while not interfering with research?
My suggestion would be to look at teaching positions (lecturer) and see if anybody at that institution would be willing to collaborate with you on a project. Of course it goes without saying that you should not expect any form of monetary compensation for the collaboration.
Edit: Just to clarify, you will have a paying job as a lecturer, working on research is something you may be able to do on the side with another faculty member.
You may find interesting the thread here Is it possible to work on physics independently outside academia?.
You do not elucidate whether the other fold was connected to physics, or family obligations. In any case you could start applying to small/liberal-arts colleges for an associated lecturer post; once this is attained, depending on your physics interests you could try finding a collaborator on a research project of interest from an other bigger institute, and take it from there.
If you had good rapport with your thesis supervisor or a professor from your graduate work, you could state your intent to come back to physics research and ask for their advice.