A quick way to stop Windows Update from asking you to reboot is to simply:
- Go to Start, Run
- Type ‘net stop wuauserv’, and click OK
This will stop the service. I don’t see this as a problem, as the Windows Update client isn’t going to download any more updates while waiting for a reboot anyway. Once you reboot, the service will start again.
Obviously this will only work if you’ve got the correct privileges to stop and start services in Windows.