What is the best way to get the anchor point to the center of a line in Video Copilot for Saber?

I'm trying to make this saber spin from the center while constantly having the anchor point between the two points (Core Start and Core End)

I prefer having to run an expression to do this but if there's another way please let me know!

Thanks in advanced!

PS: I'm using this with this current expression:

x1 = effect("Saber")("Core Start")[0]
x2 = effect("Saber")("Core Start")[1]

y1 = effect("Saber")("Core End")[0]
y2 = effect("Saber")("Core End")[1]

transform.anchorPoint([x1/y1], [x2/y2])