"Sony isn't going to make this easy for us. I was informed by Sony that even if I have a solution to fix the clock issue, they won't consider it unless I hold the patent to the solution."
Bummer! Some may think this is just be a way to dismiss your effort, but big corporations are rightfully cautious about patent infringement, and this likely is just Sony's way of ensuring they don't get into a patent lawsuit.
By the way, thanks for your efforts on behalf of the DHG users.
I am not surprised by developments. Letters to any of Sony's top executives never reach them but are shunted to an "Executive Consumer Affairs" department. From searching on the web, it appears this department seldom provides satisfactory resolutions for problems consumers present. It sounds like you may have had more success than most in that you reached more than one person and had more than a perfunctory response. Can you share their titles/positions so we might evaluate how firm Sony's stance may be? Did you actually reach anyone in engineering?
I suggest you hold off on plan B for the moment. Your plan A (or some alternative version of it) may not be totally dead. You, at least, have Sony's attention and should make the most of that. From your report we now know that Sony is open to considering a solution if there are no intellectual property issues that the solution would raise. (Additionally, since Sony is open to considering a solution, that implies that Sony recognizes that there is a problem to be solved.)
What is needed is an alternative plan A that uses IP that Sony already has access to. As a start in that direction, I think it is worth considering the user interface Sony used in the RDR-HX715 recorder that, like the DHG models, used version 8 of TVGOS. In that recorder Sony did provide a way for users to set the clock manually. Perhaps Sony could be persuaded to import the RDR-HX715 manual clock set code (which does not appear to be associated with any of the version 8 TVGOS screens) for use under the main menu of the DHG. If your contacts are still willing to have polite and professional businesslike exchanges with you, then getting them to think about this approach to the problem might prove fruitful.
Even your original plan may not be totally out of question, but there may be some hurdles to overcome.
Like you, I have had involvement with software projects (but probably not as extensively as you) but I also got exposure to patent issues when I had occasion to assist a patent attorney in a lawsuit. You might read up on patentability requirements to determine whether or not your solution might meet the requirements. If it would fail any requirement, the solution would not be patentable and Sony's excuse would be irrelevant. You might do a google search on "patentability requirements." One site I found gave a short description of the requirements:
By the way, patenting a solution that involves modifying proprietary software is not out of the question. I am certain that any good patent lawyer could write a patent application in general enough terms that any details of the proprietary software would not have to be known. Indeed, the lawyer would not want to tie the invention to a specific device or piece of software. Getting a patent might be possible but that will take a long time.
If your solution is simple as you said, then it may be obvious and, if so, would not be patentable. If someone has published a comparable solution but not patented it, then the solution is in the public domain and is not patentable. It would not hurt your cause to put your solution in the public domain by publishing its details. That could silence Sony's concerns, especially if you have not disclosed the details of the solution to Sony. (Corporations are wary of discussing inventions with inventors for fear of later being sued for stealing the inventor's ideas. If the inventor waives his rights to patent an invention by disclosing its details publicly before receiving a patent, that issue goes away.)
Of course, someone may already have a patent on it or part of it and then Sony would probably not want to touch it. A patent search that showed no conflicting patents might help remove Sony's reluctance, especially if your solution is public.
Another advantage of disclosing your solution would be that some other DHG user may read it and come up with another approach that would be totally acceptable to Sony.
Please continue with your effort to get Sony to solve our problem. I recommend approaching your contacts with the alternative plan A above or some other comparable approach. Thanks.