I've had to make a few nipples from time to time, usually from a piece of tubing lying around the shop. I've used copper, aluminum and steel refrigeration tubing.
Maybe if the steel is thin enough, you can drive an ice pick in there along side the broken stub and coax it into collapsing then grab it with some needle nose pliers, twist and pull. Try not to drive it further inside, or any metal chunks and pieces of course.