I obtained the lamp base from http://www.thingiverse.com/thing:27123 , obtained the image from http://www.scrapbookusaca.com/graphics/00000001/HTXDAH47.jpg. Using GIMP, an open source photo-manipulator, I erased the image in the center of the circle, converted that circle into vectors using Inkscape, then subtracted the circle from the lamp base in OpenSCAD.