Additionally I would then have to "continue" this linepick, from the picked coordinate, using the same vector as before.
This shouldn't be too much of a problem, as LinePick takes a start x,y,z, followed by a delta (offset) x,y,z. Once a hit has been made, you can then just do another LinePick from the hit x,y,z, and use the same delta x,y,z as the previous LinePick. That should work, right? I was also thinking about to use Renderworld with a 1*1 pixel cameraviewport.
That's an interesting idea!