Actually I think it works quite the same way, only you don't type 'x' or 'y' but choose a direction (that is, X direction means Y coordinate of the point selected)
run the LINE tool
move the cursor over the first reference point, don't click the LMB, just let the point becomes a green dot
hit the arrow key (right for x direction)
now the Y coordinate is locked, just go to the second reference point
click the LMB, the line will start at desired X-Y point
[image: 8XMY_capture_001_07112013_162805.gif]