1. It appears that you are lucky, because you imply that you just have a straight lead riser into a cast iron 90.
2. If that is so, remove the lead AND the brass wiping ferrule from the elbow.
3. If he works commercial, or get a plumber who does, he can then cut a piece of cast iron the proper lenght and lead/oakum it into the 90.
4. Caulk a new cast iron flange onto the new riser pipe.