TinyUmbrella 4.21.01 has been released to fix troubles when saving 4.2 SHSH on Apple TV. But it only works with iOS prior to iOS 4.2.1. There is no way, at least currently, for Tinyumbrella is able to kick you out of recovery on 4.2.1, since this firmware version is armed with a baseband version to check baseband compatibility, if yours is considered not update your device will stop from booting.
Remember, for iOS older than iOS 4.2.1 TinyUmbrella still able to help you in restoring and kicking you out of recovery.
Here are the download links of TinyUmbrella 4.21.01 according your Platforms: