I noticed on Server 2008 R2 that Windows Backup has bare metal restore capability. However, in 2008 it does not. Is it possible to update Windows Backup in 2008 with the Windows Backup that comes with 2008 R2 without actually upgrading to 2008 R2?
Server 2008 also has the feature to perform a BMR without needing to upgrade to R2. It's called "Windows Complete PC Restore" and it's been available since Vista / Server 2008.
For the record, Microsoft has never allowed, to my knowledge, prior versions of an operating system to have its core features be updated with newer core features. Thus the incentive to upgrade. Any attempt at hacking new features into old OSs is likely to get you into more trouble than it's worth.