Dimming aftermarket head unit on a 2005?

Forgive me if this has been asked or addressed somewhere before, but does anybody here know of a documented or undocumented wire we can tap for 12v as a dimming line in an '05 Prius?

My understanding is that the dimmer signal for the stock and JBL radios comes from the CANBUS, so isn't available to use for an aftermarket radio.

Obviously, I cannot tap into that for this purpose, but I was wondering if there was a line, like from the dimmer wheel, I could tap as an equivalent signal.

 

Thank you very much!
I'll see about doing that once I have time, and I'm up for tearing the dash back apart. This has been my one major annoyance with the head unit I'm using.

 

Specifically the first case, I know using the panel dimmer would require a lot more work, and likely wouldn't be supported by the headunit in question (currently a Dual DCPA813, needed something cheap, was annoyed by the bad quality of using a tape adapter), it'd almost assuredly need something a lot more high end, or something more custom to be able to do that.

I know it's a lot more realistic to supply the dimmer line 12v and just have it switch when the lights are on, it'd lead to some annoyances on occasion, but I just want it to know when to go to minimum brightness vs maximum brightness, and hopefully send my phone a signal to switch to night mode on the maps, since of late, neither Google Maps nor Waze likes to work quite right in that regard.