Isotrim on an Untrimmed surface

Hello, I’d really appreciate it if someone could help me figure out how I could possibly isotrim my trimmed surface without any plug-ins. Did some research and figured out its actually not possible to do that, so, how should I tackle this problem?

I split my brep using another brep, getting two trimmed surfaces. I’ve attached my gh file.

GH Help 042426.gh (71.4 KB)

You may give it a try with Mesh Inclusion + Dispatch, and for your reference.

Mesh Inclusion Grasshopper 1.0 Online Document
Dispatch Grasshopper 1.0 Online Document


GH Help 042426.gh (78.1 KB)