Found a TPU case for the Rezound with the extended battery
here.
If the pic they are using is what it actually looks like and not just using the one for a standard battery as a placeholder, then I don't know how that would work. On the Ext. battery door there is a hump all around the battery. On the picture shown in your link, there appears to be only a hump at the top, like the standard door has.
I'm a little leary buying from them, since they have no 5 star reviews, and each other level (1, 2, 3, & 4 star) each have about 100 reviews. So you got about a 1 in 4 shot of a good experience.
Edit: Just went to their site (tpu-cases.com) and the pics of the Rezound extended tpu case are the same as the ones for the standard battery. If you enlarge the pics you can see the Beats logo underneath (on the smoke case), and the extended battery door doesn't have the Beats or 4G LTE logos on it. The ext cases are $3 more, but without pics of what they actually look like, they could be the same as the ones from Mobi with the battery section cut out. I just sent them an email requesting info or pics for it so hopefully I'll hear back soon.
Update to the edit: In the description it says that the pics are for the standard battery case, and that they will post the extended battery pics on the evening of 12/13. SO they're apparently a little late.
BTW, this is the same company that made the tpu case I have for my Incredible2 (got off of ebay). The case is just as good as the ones Verizon sells, but the power button is harder to push. The reason for that is the Verizon tpu case (they call it high gloss silicon) leaves the back side of the power button exposed, so it's easier to hit from the back. The one for my Inc2 surrounds the power button on all sides, so along with the button being flush, it's also recessed about 1/16" below the surface of the case. You really gotta dig your finger in there to hit the button. Just saying.