Good news!
I had previously brought my car to the dealership and they had told me that because Honda had no published fix for this rattling issue, they wouldnt be able to do anything.
Since then I have been in contact with Honda Customer Support and was assigned a Case manager. Over the past two weeks my Case Manager has been in touch with my dealership and today was my appointment for them to attempt a fix as suggested by the Honda Tech line.
When I went to pick up my car they mentioned that it was a long process, taking over 3 hours for them to do. Unfortunately my service writeup only references my case number and doesn't go into detail regarding the fix. I asked for some more info and they mentioned that when they had first contacted Honda Tech Line support, they were told there wasn't a fix, but then the dealership said they requested the fix again and this time they received an email with what I can assume to be some sort of TSB. I asked what was done and they said they did take apart the whole rear seat to remove the rear deck and then they applied dynamat or "foam tape" as they called it between the rear deck sheet metal and the plastic. I think they also mentioned adding foam specifically to the "lip" area, which I'm assuming is the lip where rear deck meets rear window.
I poked my head up into the trunk and looked around the inside of the cabin around the rear deck, and it looks completely like it did before. But as soon as I turned on my music, i was met with the most beautiful sound. The lack of rattling is amazing! I was concerned that maybe whatever they did would "muddle" or dampen the sound of the subwoofer but I can't say that it has. It sounds very similar to how it did before, except without the rattling. In one song that I tried so far I even noticed extra bass notes in the song that I hadn't previously recognized. It seems that the subwoofer now may be more responsive, but thats probably just a result of the rear deck having more mass and a sturdier foundation for the subwoofer speaker.
I have to say I believe my problem is fixed!
If you are experiencing this issue, please contact Honda Customer support, describe your issue, get assigned a case manager, and then hopefully your case manager can work with your dealer to provide a fix. It took me just under 3 weeks from initially calling Honda Customer Service to setting up this appointment and having a fix applied.