Universal Update Tool (script help needed)

I've created a Windows PE boot disk and edited the Startnet.cmd file to launch a batch file which runs 4 versions of command line scanners.
Has anyone scripted an autobatch update for the primary AV vendors?
Sophos, Trend, McAfee.......?
Since this is a PE image I have to mount, edit and unmount to update the image.

Please let me know if anyone has a quick script that pulls down all the updates? Then this can run as abtach file at night and in the morning the files
will be ready, if we need a USB boot scan.

Thanks,
Gregg Dotoli