Layer starting point setting in spiral vase mode

Hello,

I would like to print a thin canopy for a airplane by using translucent PETG. The spiral vase mode is doing the job, but the starting point of each layer should be at one of the end of the canopy not somewhere in the middle because this leads to a visible seam. Would be great to be able to set the startpoint somehow to one of the corners of the part.

Thank you very much.