I think, going by the RaW, this ability only works with round spells. I base this assumption on the line saying, "the spell's area is centered where the arrow lands", not something along the line of "extends from" or "continues along the path of".
But being the generous GM that I am, I might say a good hose rule could be that cones begin where the arrow lands, but must face in the direction the arrow was headed, or that the line continues along the path of the arrows flight. (Could not shoot arrow 50' feet to intersection in underground dungeon, then have the lightning bolt go left)
(fire arrow)------path of flight------(hits here)====== lightning bolt 120 " ====
Or
------------------------------/ x x x x
-----------------------------/ x x x x x
=====path of flight====(hit+Cone x
-----------------------------\ x x x x x
------------------------------\ x x x x
( This graphic looked better in my head, but didn't translate well into text, had to use hyphens cuz spaces didn't show up and the lines set themselves to left margin)
