Good to see you've got it working. Just one small point - WSUS doesn't push anything - it's a completely "pull" technology. The server pulls updates from the MS web site and stores them. Clients then "pull" a list of updates from the WSUS server, check for what they need, pull those updates and then notify the server of what they've done.
the point about sysprepping is a bit of a red herring; you do need to sysprep machines before imaging but that doesn't fix the WSUS ID (although there's nothing to stop you adding the commands that @fn-gm has posted to cmdlines.txt in sysprep so that it gets cleaned up)

