I was wondering if anybody has a resolution to a broken Nut on a sink extension

From the wall is the drain extension is connected to the trap. The problem is the nut broke off. Now I can't slip a new nut over to connect to the trap because there is a solid ring from stopping me from replacing a new nut!

I was going to cut the drain extension shorter and try to get something going but there might be an easier way..

HELP!
I will very grateful as plumbing is NOT my thing!


Diagram it is the
http://static.howstuffworks.com/gif/...ed-drain-2.jpg

Ace hardware carries a replacement nut that disassembles. The nut is 2 halves with a clip that holds it together