Here's another alternative that worked great for me.
Do step one from the OP above. Then use the built-in browser to find a link to Go Launcher from the Internet (try here
first, but I'm sure there are others if that doesn't work). Download and install the apk file - despite Amazon's customized skin, it's still built on the Android OS, so it should install any issues. Then just run it to start the launcher, and from there you can set up a more or less standard Android environment with about 90% of the 'normal' functionality of a tablet (aside from the lack of camera and other physical features, of course). If you set up Go Launcher EX as the default app for the Home button, it acts mostly like a straight Android tablet, and you haven't invalidated the warranty. You can't link it to a Google account and get those apps, but otherwise everything else is pretty much the same. Use Titanium Backup or ROM Toolbox (or just direct sideloading) to copy apks for the non-Amazon apps you want to install, or just download them directly from the Internet. I assume this would work with other launchers, too, but I can only speak to Go from experience.
The really slick part is that you can still run the original Kindle Fire environment as an app itself, so that doesn't go away.