The first thing you need to do is to get a license from Adobe to distribute the Flash Player. This license is free, and the steps to acquire it are described here.
There are two ways to make use of this update once you receive the link from Adobe:
The Adobe link includes directions for using what they refer to as an SMS Catalog. If you download the file, you can use File/Import Catalog in LUP to automatically create the update. The downside of this approach is that it isn’t possible to customize the install.
Warning! Using this approach, the update will (most likely) be immediately approved for install for All Computers. If you want to test this before rolling it out to your entire network, you will either need to use the manual steps (below) or quickly change the approval for the update after it is created.
It is possible to disable the autoupdates for Flash along with other settings. In short, create the mms.cfg file with the parameters you want in it, then distribute the file to %windir%\system32\macromed\flash (not sure about x64). In order to create this file during installation, see [Creating_Configuration_files_during_installation.]