Vertical Line: one endpoint fixed, other to edge of graph

Is it possible to create a vertical line, somewhat similar to v_line except one endpoint is fixed.
or is there a clever command to trace always go to edge of graph?

imagine something that would look like if you could set the y0 and y1 like:
y0 with ‘yref’=‘y’
y1 with ‘yref’=‘paper’

the nice part about the v_line is that the annotation is always in the same position regardless of zooming in and out.
But I can’t have the line cross the entire graph.

Not sure if I understand the question, but v_lines are annotations. You can create them manually, here an example: