Quick answer: Yes, I have the heated seats (I get the impression that you can't really get the leather seats without seat heaters, but anyone feel free to correct me if I'm wrong), and the heater element is essentially "built into the leather seat cover," like it's "sewn in" right below the leather you actually sit on. So, my extra padding went below that, and there was no affect on the performance of the heaters at all. "It's all good."

Longer answer: I dug up my photos of the situation, so let me share those with everyone.

Here's the "before" picture, with red lines right about where I was feeling the "wiring harness" bumps:



Actually, they were probably a wee bit farther "back" on the cushion than that. I suppose I should add that for some reason, I actually DESPISE what you'd call "lumbar support" -- I dial it all the way out. Thus, I would sit "farther back on the seat cushion" than I would if I had a bunch of lumbar support dialed in.

Next up, here's the "mobile truck" that comes to my dealer's lot:



The proprietor has been in business since 1979, so he's vastly experienced. He did an excellent job, and the price was lower ($100 for all labor and materials) than I ever imagined this kind of work would cost!

The truck is basically a "mobile work bench," and here's my seat up on that bench. The pink foam is the stuff he's going to cut and push in there between the existing cushioning material and the leather seat cover:



Note the clear-plastic connector right next to the seat belt receptacle -- that's part of the system that attaches the leather seat cover to the seat frame. The "seams" down the center and between the cushion and the bolsters are held down with hog rings.

Here's where he has cut the pink foam into two sections that'll fit between all of these seams. Essentially, he just cut to fit, then sprayed glue onto the existing cushion material to hold the new foam in place:



Again, the seat heater is built into the leather seat cover -- this modification didn't change its performance at all.

Here's the final result -- can you see the difference between the driver seat and the passenger seat, or this "after" picture compared to the "before" picture, above? It is indeed a little "overstuffed" compared to the original. Oh, and apologies to the folks who might be gagging at the sight of that XLE "fake wood trim." I actually kind of like it.



Oh, and this is "bisque" leather, though the color you see in photographs is very dependent upon the available lighting at the time any photos are taken....

So, in review, here's what the guy did:

1. He pulled the seat from the car (about two minutes with an air wrench to undo the bolts, then he unhooked the wiring harness, and it was outta there).

2. He pulled off the connectors holding the seat cover to the seat frame.

3. He removed enough hog rings to get in there and start working.

4. He cut foam to fit in between the center seam and the bolster seams.

5. He applied glue and fit the foam in between the cushion and the seat cover.

6. He actually worked some white-colored foam (about half the thickness of the pink foam) around those pesky wiring harness bits that were causing bumps in the seat, to further cushion them.

7. He popped in new hog rings, reattached the clips to the seat frame, and got the seat back together. It was actually a very tight fit -- there's only so much "play" in the leather to go around this extra padding, so he earned his money trying to get that to go back together again.

8. He put the seat back in the car -- again, simple and easy.

We made the arrangements to get this done a week earlier -- he quoted me "it would take an hour, for a hundred bucks," and that's virtually EXACTLY what it came to -- one hour, and he charged me $100. Compared to fighting with seat cushions and such, this was an incredible bargain as far as I was concerned!

The result has been pretty darn good -- I had this done a couple of months ago, so I've had time to get used to it and evaluate it. "More padding" is definitely a good thing, and this sure evened out all of the "bumpy stuff" I was feeling at the back of the seat cushion, including that center seam. I certainly tried a bunch of aftermarket seat cushions prior to doing this, and spent considerably more for that junk than this cost me -- and, of course, this beats anything like that hands down.

A lot of folks who I've described this to have thought I was crazy, or had some kind of hyper-sensitive butt, but I have indeed run across a few folks who have complained about the very same thing I did -- how, between that center seam and the bumps from the seat heater wiring harness, the rear part of the seat cushion was just uncomfortably bumpy. This absolutely solved that problem, in spades! And I hope this write-up might help any of you who've been a bit unhappy with your leather Camry seats -- any competent upholstery shop should be able to make this same kind of modification to your seat.