It could be done relatively easily, as long as the car is FWD or you convert AWD to FWD (which is easy enough, but removes the AWD).
The Ford Five Hundred came with the exact same chassis/drivetrain, but with the 6-speed Aisin as an optional transmission. You'd need the following: transmission/drive axles/PCM/top motor mount/one bottom mount/shift assembly (not the entire thing-some parts can be reused), and a new oil cooler. All of those parts are available used for very cheap. Then, you'd have to have the ECU reflashed (that's a workaround for this is you change the smart junction box as well).
I researched this pretty heavily when trying to buy a used FS with a dead tranny for very cheap (1K)-but the deal fell through. One thing to note, however is that parts are now available for the CVT transmission--and the CVT is actually quite durable. The issue is that if anything goes wrong with them, most places won't fix them. I have 150K trouble-free miles on mine and it behaves like new. The most common issue on these is failure of the input shaft (and often times just the input shaft o-ring). If you catch it early (as soon as it starts making a 'helicopter-type noise'), you can often fix the transmission without too much trouble.
So, there are a few different options should you have transmission trouble if you're willing to dig in yourself--but I think the stock CVT is actually pretty reliable as long as you don't dump the wrong fluid in there.