That's a good question.

You might be able to use the "underBits" property of View to determine exactly which part of the character is touching the control line. If I remember correctly, underBits is a heap pointer to a chunk of data relating to backgroun, priority, and control data. Another possibility is simply to determine which direction the ego was headed and about where it touched the control line. For instance, the below image:
............
.........../
..._..._../.
../.\_/.\/..
./..........
.|..........
/...........If this was a control line, I would only need to know about where the character was on the screen, and the direction. Since you know the control line contours, you can make a "grid" system and detect the collisions yourself, more or less. Course this may be more trouble than it's worth if SCI has this ability already.

(Edited: if you read this post before I modified it, I apologize. I misunderstood what you meant.)