There are various ways of tackling this. One is to go to the feature tree in SW, right click on CAM part and select "Edit Part". Then select the top face of the part, right click and select "Insert Sketch". Once in the sketch select the edges you want to form the profile and convert the entities to sketch lines. Stop editing the sketch, go to you SolidCAM job and define the profile from the sketch you've just created. Voilá.
Another way is to open up the CAM part for editing, select (or create) the plane which bisects the part at a place where the profile is as you want it and ceate a sketch. Then via sketch tools selrct "Intersection Curve" and pick the faces of the profile. Then define the geometry as before.
The CAM part is a very powerful tool in defining geometry and opens up all the usability of SolidWorks for controlling the tool path. For example, setting up a work area or constraint boundary, offsetting a face and filling it to act as a mask in 3D machining. I'd be lost without it.