Change default anchor point position


Hi there
I am having difficulties with pinning an object at the top
It appears that Natron uses Bottom Left as 0, 0 coordinates, but I am wanting to pin at Top Left
The reason for this is that I am read images in of varying height at render time, but want to have them all pinned at the same level at the top of the canvas.

Has anyone got any ideas how I can either
A) Change the anchor point to top Left
B) Read the image height of the dynamic images and then change the anchor point accordingly

I hope that makes sense
Many thanks