Ah, in that case you should be able to just get the location of your playercamera and subtract a few Z units depending on how far down you want the trace, and use the same forward projecting trick I mentioned.
You can enable debug drawing to render a line between the points and just adjust your Z offset until it comes from where you want. I’m not sure about a way to convert between 2D screen space and 3d space. I think I could figure it out in the material editor but not the blueprint editor.