Andy, you are correct about ViX, but stop apologising for the person that imposed this restriction...
I have historically couch flashed all my boxes (ET8500, SF4008, Gigablue 4K, Mut@nt HD51) and have never had an issue ..... unlike usb flash..... and I couch flash at times several times a day when I am testing something... without failure. On the HD51 there is even no need to flash over the current live image, so what is the problem?

Usually I keep quiet but this situation is down to a lack of understanding (I believe) in how ofgwrite works... and the person concerned should re-evaluate his position.