Make a hole by heating a small area on the side of the bowl while blowing hard. It will pop a hole through the side. Heat a larger area of the bowl where the hole is. Unfortunately the hole wants to get larger. Make another hole on the side of the bowl for the carb.
Some people use a corbon rod to block air escaping the first hole.
Hold the pipe with a curved tweezer. Heat the mouth area and pull the glass thin. Break the glass with a wire cutter plier. Trim as neat as possible. Heat the mouth area to smooth it out.