There are sensors that detect when the media is "out", and they can be tricked to think there is media loaded... but without going into that, I have printed onto clear film before, though that was on an SP-540. I suspect it is not the sensors, but perhaps the pinch roller isn't on the grit roller?
With all that said, I have to let you know, my experiment printing onto clear film was for the same purpose, printing a film positive. I can tell you that our results were that the Eco-Sol black ink does not have the opacity required to produce a film positive, even on waterproof film. After printing on the film, I held it up to the light and was able to see right through it. This is not the printer to produce film positives.