I think the bottom line is ,Mastbender is right otherwise it could be a dodgy fix.
Extending the pully end is totally possible with a carbon boom if you know what your doing but not with an alloy boom unless you really know your alloy welding.
I would think breaking a boom while sailing is not very much fun.
Personally i also would look for a rough looking ( cheap ) second hand boom and re grip it. A early Christmas present to yourself , thats what i say to me .