How to drape a polygon vector shapefile onto an arc grid image

I have created elevation model form an arc ASCII grid file using the command 'arcgridread' and am also able to visualise it in 3D using 'mapshow' and an appropriate colormap. I also have a vector polygon shapfile with projection coordinates for the same area (that shows boundaries of many polygons)and can independently view it by using the commands 'shaperead' and 'mapshow'. However, I cannot seem to find a way of draping this shapefile on the dem in the Mapping Toolbox ... Anyone with ideas on this?