Tracking text masked by a BSpline node

I am trying to track some text behind a shot of a viaduct. I have managed to mask out the viaduct (foreground) by using a BSpline node on the Text node which is successfully hiding parts of the text behind the columns of the viaduct in my reference frame.

However, when the video is played forwards or backwards, the BSpline isn't following the tracking which is already tracked in a PlanarTransform node, connected under the Test node.

Is there a way to create a mask that is tracked with a PlanarTransform? Or a better way of doing this so that the mask drawn follows the movement of the video?

Thanks!