This post should really be in the XTensions forum, as basic Quark users will never have seen the BRQ!
You can switch off picture printing via the picture usage box, but that may be a pain if there are lots of missing pictures.
I recommend you go back to Emsoftware again and re-explain. Also, your boss should take on board any critique offered, as they are always helpful and have not done it to be annoying. The advice will be good. They may have misunderstood the question - be friendly, they are very nice people!
I know nothing about your workflow, but it occurs to me you could create a blank image with the correct name which you could overwrite with the correct image when you get it. That way XData would happily place a blank and think it had found it, and then no question mark.