The study I linked to showing the effectiveness of Ivermectin was only done subcutaneously. I did not find a study on the effectiveness of non-subcutaneous Ivermectin treatments on screw worms.

Given one of the areas they focused on the study is the scrotal area post castration, I don't expect that a pour on would cover that area well enough to be an effective treatment. Happy to read other studies if you have them showing otherwise.