Thanks for the suggestions. Both methods get the desired result but I think Keith's approach leaves you with cleaner-looking polygons (subdivide creates some nasty looking ones). I still think it would be convenient to have Knife functionality in the vertex modeler but I imagine that is somewhat unlikely given the focus on Amapi and the Amapi-Carrara bridge (which sounds great but one of the big knocks on programs like Lightwave is the separation into two programs so in some ways this is like a step backwards). Personally I think there's still a lot of mileage to be gained by adding functionality to both the spline and vertex modelers inside Carrara as well and hopefully the folks at Eovia agree!