How to deploy software with better user experience

We need to deploy an application to all of our computers. During the installation, the applicatioin will disconnect network for a short period of time. It also need to reboot after installtion. We want to give our users better experience than using group policy. Does anyone implement the installation as follows,

1. Before application starts installing, we want to prompt user to save and close any working documents. User can defer the installation, but should not be able to cancel it. The application can be installed only when user agrees to install, or when user log off the computer.

2. When installation completes, prompt user need to reboot. User can defer the installation, but should not be able to cancel it.

We have tried 'defer task' and 'defer reboot' functions in NS. However, the task/reboot will start if user does not repond to the promption. This is not what we want.