I think it would allow you to see his outline. To reference my post below, if Bilbo's body is keeping the ejaculate from touching the ground, it would be invisible because it would be under the same effect as clothing. But you would be able to see any ejaculate that fell to either side of him and where part of it is suddenly missing. That was always my interpretation of the mud or water thing, the parts that hit them go invisible, and all you see are the parts that don't go invisible around them.