I'd say that if you're willing to extend your contract and pay the 2-year contract price for the phone, you've got a MUCH better chance than if you were simply asking for a switch replacement.
A lot of time with new phones they will have special promotions that allow people to upgrade early if they agree to those exact conditions (phone at 2-year price w/ contract extension). I know because I've done it a few times before. The fact that you also want the brand new model will also play in your favor, because those are usually the devices that these deals qualify for.
For what it's worth, I've always done this over the phone, as I don't live anywhere near a VZW store.
Not guaranteeing you anything, but it never hurts to ask.
My daughter got the Tbolt a month before me. She seemed to have a problem with the first one (wouldn't connect to 4G even after a software update). They sent her another one.....same thing.....then sent her another one, this time, the 8MP camera didn't work. I told them they should just send her another brand of droid (Charge was almost ready to come out), they said "No, we can't do that".
Keep this in mind....the insurance REPLACEMENT cost for the TBolt is $100...not $50 like the 3G phones. My screen cracked and was going to get another one and pay the $100....but I found a place locally (San Jose) that would do it for $105. I ended up going into VZW for another issue and they determined that it was THEIR fault and sent me a refub TBolt for free.
If your button is pushing into the case and that is your only issue, I would find out how much it would cost to repair it instead getting a replacement phone. If you have the money to upgrade to the Bionic or Vigor.....go for it!
It is a very different story if you're asking them to replace a defective phone with a different model, as opposed to asking for the ability to upgrade early.
As far as the repair route, I KNOW I've seen a youtube video or instructions somewhere on how to fix the exact issue the OP describes. I don't have a link for it, but I know that there is a DIY fix for it. I also remember thinking, "there's no way
I'm taking my phone apart to that extent!"...but for some, it is an an option that may cost you next to nothing (if successful).