If I was to install subs on a bose HU, I would attach them to the bottom of the head unit using duck tape and super glue, then shoot some spray expanding foam into the cd slot so as to eliminate any vibrations from the deck. then mount the whole unit to the rear bumper with the sub firing up, this will eliminate any standing waves from developing in the car, again, mount it using duck tape and super glue. Also be sure to put some stripper glitter on the woofer cone, so as to make it act as a reflector when the tailights dont work.
aww common bose aint that bad for stock i know you not a caddy fan but if u ever get the chance sit in a 98+ Seville with the bose 4.1 system. it really does sound great