Just calculate your total distance for the entire segment, get the ratios of each individual segment per total length, which will let you know what 'uv' distance each segment is. From there you can carve(with the sop)the specific segment in which your target uv is lying.
To build something around this in order to mitigate that behaviour would surely negate the slight performance advantage the carve node has, right?How do you know the carve sop has better performance when it's not doing what you have with vex?
Did you try comparing a single segment with vex(only two point ends) compared to the carve sop?