Gah! Changing odometer reading?

Short version of the story: A tree recently gifted one of its branches to my 08 Gen 2, punching a nice hole through the windshield...while it was raining. After getting the glass replaced, I discovered several electrical problems with the car. The rain damaged the speedometer unit, killed the radio, and the power port under the radio is dead too (even after a fuse change). Yay.

One trip to the local U Pull It and and afternoon of monkeywrenching later, I replaced both with used parts. That, it turns out, was a mistake. My Prius, at the last oil change about a month before the windshield broke, had 209,5xx miles on it. My new odometer? 414,230. Based off the mileage recorded on my last state inspection, I'd have needed to drive around 25,000 miles a month to pull that one off, but NO car buyer is EVER going to believe me if I tell them that the real mileage is only half of what the odometer says.

Which brings me back to the question in the title. What does it actually take to change the odometer reading in a Gen 2 Prius? I've already looked it up, and it's perfectly legal for me to change it in this situation.

 

Called my local dealership yesterday and they weren't particularly helpful. Because they didn't pull the old unit out, they can't (or won't) reset it for me. Even if I take them my old one, they said I can't prove that it came from my vehicle, and even if I could prove it, the number would no longer be accurate because I've driven it since the swap...and they won't program it to an innaccurate number. They said they could reset it to zero for me, but would have to place a large sticker in the drivers door frame showing that it was reset and that the previous mileage was "unknown". While that may be slightly better than 400k+ miles, it's still going to be a big problem when I try to sell it.

I was hoping this wouldn't be to difficult to just do myself. I do have Techstream, but I wasn't able to find anything odometer related in there. Google searches have turned up nada on the Prius odometer.