Good news, everyone! smwoodward posted a working method on xda-developers to downgrade an Incredible running 2.2 to 2.1, even if it was un-rooted. The original thread is here. However, he didn't have a high enough post count to link to files directly, which makes it a little harder to follow. Another forum member mirrored the instructions on his blog, including links to the necessary files. I can confirm that this works (just did it). One thing to note (that the mirrored guide doesn't include) is that you have to have HTC's adb drivers installed; you can do this either through unrevoked (instructions here) or by installing and then uninstalling HTC Sync. I think the former is easier ... I'm also not sure if you have to use a specific version of HTC Sync for this to work. But anyway, FREEDOM!