Split will only use straight lines, but you have a good idea. I will pose it to our designers. But for now you must use different methods to achieve what you are after. I have 2 ideas and maybe more experienced users have other ideas.
A. Use the
Subtract from Polygon and Magic Wand to remove the unwanted portion of the slabs. This requires that your perform the operation on each slab individually.
OR
B. Convert slabs to a Morph element and use boolean subtraction to remove the unwanted portion:
1. Select all slabs and
Convert to Morphs.
2. Then use a
Union boolean operation to make the multiple Morphs into one.
3. Use the line tool and make an enclosed shape with the arc.
4. Use the Morph tool and space click the enclosed shape you just made.
5. Extrude the shape to intersect the Morph slabs.
6. Use
Subract boolean operation to remove the unwanted portion of the morph. The extruded arc Morph will also be deleted in the process.