blending an edge for a relief carving?

[myxpykalix]

What i am doing is the supports indicated by the red arrows may have some type of 3d relief carving in it but i need to keep the ends the original width of 1.5" so when i carve my 3d relief I want to make, for lack of a better term, a valley where the carving will sit and gently curve back to the 1.5" width, but i'm a little unclear on the best method for this.

I don't want to make any kind of dish, or cupped area for the carving but a gently sloping shape. My initial thought was to do a 2 rail sweep with a vector outline "placeholder" for the 3d carving in the appropriate place.

I haven't thought this entirely through because i'm not sure how the placeholder would interrupt the sweep.

[navigator7]

Jack,
In my solids program, you create the solids you want. Place everything where you want, then subtract where the solids overlap.
Does that make sense?
I'd export the resultant file as an stl.

[steelhead]

What software do you use jack. both for cad and cam.
FYI, If ever needed I can be of help with auto cad (I use it for line drawings and solid modeling) and cam software FeatureCam. (4 axis simultaneous ) and part works.