After running the silent install from the MSI file:
MSIEXEC /i "%inst%\source\VSE800.MSI" ADDLOCAL=ALL /qb
Search for a file called mcupdate.exe. This file is found in different locations depending on the version of McAfee you are working with. I found v8.0 to be in C:\Program Files\Network Associates\VirusScan\mcupdate.exe and v8.5.0i to be located at C:\Program Files\McAfee\VirusScan Enterprise\mcupdate.exe. After finding the file run mcupdate.exe /update /quiet. This command line can be used to run after your install to force the client to update immediately.