Upgrading NetBSD in-place in a clean way

[Stefano Marinelli <postnet%dragas.dyndns.org@localhost>]

Ok, let's suppose I want to upgrade a NetBSD machine without rebooting with 
sysinst and without having the possibility to use the build.sh script with the 
sources.
I'd do something like that:
1) download the daily (stable, for example) binaries (for example from 
http://nyftp.netbsd.org/pub/NetBSD-daily/netbsd-5-1/)
2) Untar all the sets on the file system I want to update
3) run etcupdate
4) reboot

Tried that in a test virtual machine and seems to work. But there's a problem: 
what if something has been removed? Untarring the sets doesn't remove the 
(stale) old files, while the etcupdate just deals with the config and startup 
files.
Is there a cleaner way to do it?

Thank you!
Stefano