Although BART PE builder can be used to create a new iso image with custom plugins, I do not believe you can use it to add to the Avast BART iso. Even if you extract the iso image, you still need to have the source install files. Also, how would you maintain the Avast setup AND add the additional utility?
It would be great if Avast would address this issue. We use SafeGuard Easy to encrypt our notebooks. I am inclined to stop renewing our subscription since I cannot scan these drives. SGE provides the files needed to create our own BART CD, but I cannot seem to add the Avast. Likewise, I cannot seem to incorporate the SGE into the Avast iso.