Another, and perhaps more practical, approach would be if one could insert the Vray (or other material's) model just like usual, and then every time this has occurred or after one has added a number of foreign material items, one just run the converter script again.
However, for some reason this doesn't seem to work. I don't know if it is because it not supposed to be run twice on the same scene, or if it has something to do with either the model or the way I imported it, but it doesn't appear to work. I get an error message saying Material type "VrayMtl" not supported and it then list an offending material.
Is this something that either be fixed, or a possible way forward?