Creating hallways on a stadium

Hello everyone,

This can either be very simple or very complex but either way I'm not able to figure it out.

I'm creating a definition in which, starting with a geometry on the plane, it creates automatically the grandstands surrounding it. This is working quite well but I'm having lots of troubles creating the vertical staircases.

I've tried already perpendicular lines from the starting geometry that, using "Crv CP" Curve Closest Point, erases those seats that are closer to it but it dint end up working well at all.

As you will be able to see in the image attached (Grandstands1), I have perpendicular lines coming out of the initial geometry and those indicate where the staircases/vertical hallway should be. Basically the seats closest to those lines should be erase to create a gap that represents the stairs.

Attached is the Grasshopper document so you can have a more clear idea and also I attached the Rhino document  with the initial geometry that I'm working with.

Does anyone know how could I solve this problem?

HELP and Thank you!