I've removed the stock tube from the sending unit before. Then I remade a new one to the size I wanted. In your case a steel 1/2" line formed to the stock shape. Open up the hole in the sender and silver solder to tube in place. A tab is welded on the inner side of the sending unit to keep the 1/2" tube in place. On mine is used the finest media to blast clean the assembly and give the outer sending unit area a light coat of clear paint to keep from rusting up.
After posting this I realized that when I did this, I was adding a second line for fuel injection purposes. You could add a second line too and plug the original. Keep the original one inside the sending unit to act as a support for the new line. For fuel injection I use the stock line as the return line and put a bend in it to direct the incoming fuel from the outgoing fuel.
i also did almost the same as Shane. I used the factory 5/16 for my return and drilled a 3/8" oppsite and brazed it in. I also bent the same as the factory but I brazed them together. Only problem I have is if the tank is around 1/4 to empty and I take off fast or turn a corner quick the fuel moves away from the pickup and the car will stumble.