What about this, you could write a script that looks at the already working relative paths and loads that in to a new container field.
Just a thought.
Yes, I suppose that might work. But it turns out that the solution was quite easy, and one I should have thought of earlier, I changed the calculation field to calculate an absolute path. Curiously, the image does not appear on the host machine, but it does appear when viewed through IWP! Curious...