Create a copy of iTerm called iTermVisor which will run in background on login, only uses visor.

iterm2visor.sh

create-visor() {
    local p='/Applications'
    cp -rf $p/iTerm.app $p/iTermVisor.app
    mv $p/iTermVisor.app/Contents/MacOS/iTerm $p/iTermVisor.app/Contents/MacOS/iTermVisor
    defaults write $p/iTermVisor.app/Contents/Info CFBundleIdentifier com.googlecode.iterm2visor
    defaults write $p/iTermVisor.app/Contents/Info CFBundleExecutable iTermVisor
    defaults write $p/iTermVisor.app/Contents/Info CFBundleName iTermVisor
    defaults write $p/iTermVisor.app/Contents/Info LSUIElement 1
    rm -rf ~$p/iTermVisor.app
    mv $p/iTermVisor.app ~$p
}