this (lack of an obvious naming mechanism) was the reason i came up with my vbs and custom token system for the unattend file. however, my methods won't work for you directly... we name our machines using their serial number, not their physical location, so it's really easy to do it unattended - it's just a wmi call. then again, it probably wouldn't be too hard for you to have a machine prompt for a computername via VBS right after it finishes booting into winpe, then store that in a file on the ramdrive (X:), then use that later on to populate your unattend file using token replacement. i also use these custom tokens for setting the time zone based on which pxe server it booted from (dunno if you can still do that in 7.1), and also injecting a few items into the system properties screen - it now shows you the model name and date the machine was imaged when you right-click Computer and hit properties.
prompting during a build sure stinks though - rather takes away from the whole "automation" aspect of this platform.