Geometry.Split using 2 surfaces as the tool, please help!

Hello!

Here is a plan view diagram & 3D view

image
I am trying to use two surfaces that are perpendicular to each other to split a right corner geometry.

My problem now is I can only split the geometry with one surface at a time resulting in four geometries, none of which are my desired result geometry (the corner).

When I try to combine the surfaces into a polysurface and split the geometry with that I get this error

Does anyone have any ideas on how to accomplish this in one split rather than having to sort through and combine the results of doing two splits?

Thanks in advance for any help!

bump

Springs has a node called ‘split recursively’ that may help here.