I'd leave the fitting in there, cut the broken part flush with the rest of the fitting, and epoxy a thick disk of hard plastic over the top. Then drill and tap that. No big deal if it doesn't work, you needed a new fitting anyway right?

 

Whatever adhesive would need to be compatible with gas..

Find the fitting and fix it yourself:
http://www.harborfreight.com/welding...c-welders.html

 

Here is an interesting how to video on plastic welding I found that may help...

http://www.youtube.com/watch?v=I2pQKPxZMd0