I have a Camry hybrid and have done this hack, and it does work.
The following is a post I made after I got mine to work.
"I was having a problem making a "hybrid" navigation DVD using the loading.kwi file from the 5.1 version. I think I made about 16 DVD +R DL Coasters. I tried using Nero, Ones, and a couple other burning programs. No dice. This was using my Sony DRU700A burner, and it kept giving me write errors, so I bought a Samsung DVD Burner (Re-Badged as a MadDog Writemaster) and it was able to sucesfully complete the burn process, but it always taged the DVD as a DVD +R DL and not as a DVD-ROM wich is what the Denso Navigation DVD drive reads. I tried changing the booktype to DVD-ROM, but that is how the drive was set from the factory. So back to the store it went. I then got a BenQ DW1650 (Rebadged as a CompUSA drive) since it got high ratings on cdfreaks.com, and the first burn I made was read by the Nav's drive, and works great. Now I just have to cut the power to the Nav so it will load the old 5.1 file, and I will have the 6.1 map data and the 5.1 override.
As a side note, since I was having so much trouble burning a good hybrid disk, I tried to make a direct copy, and using the Sony and MadDog drive, was never able to make one, but a coworker has a DVD duplication device (kangaroo replicator, it makes up to 5 copies from a source disk at a time) and it made a good backup copy. The burners in that machine are NEC drives, and the source drive is a LG drive.
The working Nav Hybrid disk was riped using Prassi ONES in the DVD incremental - closed session with ISO 9660 + UDF with Fast Disk setting.
The disk name was the date the disk was made, but if you want to use the original disk name, the 6.1 is 464210-0629 and the 5.1 is 464210-0791. The disk name does not matter, the nav does not read the disk name.
I also used ImgBurn to ensure the Booktype for the drive was set to DVD-ROM, as this is the only way the car can understand the new disk.
A BIG thank you to all those that have experimented to discover this workaround, and a BIG thank you to those that helped me."
From the following post:
Overriding hybrid navigation system - GreenHybrid - Hybrid Cars