I have been using YUMI to create a multiboot usb flash drive and putting a few AV distros on it then booting up in each one, running a distro, then going to the next distro on the windows boxes in our house. Its a bit of a chore to not only DL/write updated versions of the AVs on the drive but also to boot up and run each distro.

My question is has anyone come up with a way, or even better is there a distro or live linux installer prog that can create something with up-to-date AV defs and can be run from command line so that they could just boot and automatically start scanning (even better just reboot and start scanning with the next distro if nothing is found).

Any help would be appreciated.

I'm curious as to why you want to boot multiple distros?

Anyway, the only way I can think of to do exactly what you want is with Grub. I'd have each distro run a script on startup that goes through the scans and then runs grubreboot:
https://wiki.debian.org/GrubReboot

You'd have to do something similar for updating your AV signatures.