Wert,
The recommendation PSGuru provided is the method built into patch management and sounds like it will meet your needs.
What you may not have noticed is the "Notification" tab at the top of the policy screen. This tab gives you the option to customize the messages presented to users and the ability to authorize users to defer the updates and/or reboots for x amount of minutes, hours, days, etc.
Don't forget you can clone the policy and assigned different policies to different machines. For example, you probably want different reboot policies for servers than workstations.
NOTE, Symantec uses the terms "Patch Management" and "Software Update Solution" interchangably so it can be confusing. The sofware update plug-in policy is what controls patch management.