Well, I managed to answer my own question. I cut out a big chunk of the drywall and gave the toilet a big bear hug. That way I was able to get an angle to knock the new pipe into the tee. Sweated it and everything looked good. I turned the water back on. There is now a leak at the bottom of the tee (old connection). Oh well. I guess I'll have to cut out the tee. Something tells me you can't just add and remove pipes at a sweat tee without replacing the tee entirely... live and learn. Will I be able to find a replacement tee with longer "stems" for when you had to cut out a previous tee? If so, that will help me avoid the work of having to cut back and couple the pipes.