just heat the glass in the places that residue is present and blow the smoke out. after the glass cools, soak it in rubbing alcohol for about 10 minutes, rinse, then scrape anything left over out with a safety pin. works great for me.
Also, (what I've seen tweakers do) Q-tips and Tooth Paste work well, if you don't have IPA. Further, Arm & Hammer should do the trick, as long as you keep the consistency thick.