I want to make a slit into this mesh, how?

Hey,
I created this spine-looking shape in grasshopper. I want to make a slit into the rotating base curve before printing this and inserting a LED-strip. I tried some things, but I can not seem to make it work. Anyone that knows a way to get this going? It is basically a u-shape slit that I can then after cut out with boolean difference, I guess? The tricky part for me is mostly working on the mesh to get the right placement everywhere and so the correct depth of the slit.
!Scoliosis!.3dm (4.1 MB)