There are a couple of things that spring to mind based on some experiences I've had.
Firstly, even though my resume says PM, I get approached for developer roles all the time (probably the CS degrees pattern-matching recruiter bots). Have you tried applying for a developer job at all, just to see which hurdles might be the hardest for you based on your experience and current skills?
Secondly, there are some roles that might be a good transition from PM to developer that would allow you to get the best of both worlds. Developer Relations/Evangelist comes to mind, Technical Project/Product Manager, and similar.
One thing I would personally do if I were making this transition is focus on building out a personal project, putting it on github and becoming active in the relevant community (whether it's stack overflow, irc, reddit, pull requests, etc). Contributing to open source is commonly recommended, though not something I'm particularly involved in. I would personally stay a generalist as that's something I enjoy and part of why I became a PM in the first place, but YMMV.
You could potentially find ways to code as part of your PM job. I knew PMs who committed patches to the main product, and I managed to find several ways to write code (internal hackathons, test apps, etc) when I was working on our developer platform.
Also, I'd recommend you look at Hacker School, if a sabbatical from work would fit into your plans. There are also several "programming bootcamp" in-person courses which are aimed at placing graduates into engineering jobs, but these are probably beneath your current skill level.