oh ****! pinion shaft retainer bolt snaped!!

there's no way you can drill a hole in the bolt shank and get an ez-out to that bolt is there...?

and this may seem like a dumb question, but were you turning it the right way? i've taken out that bolt several times and never broken them...almost rounded them out, but never had one break on me...
 
Had something similar happen to me before. Turned out a piece of it snapped off and lodged in there allowing me not to get the shaft out. Ended up ruining the carrier in the process but I had no other choice. I bought a spare carrier rebuilt that off the car and just reinsalled that. Just had to reshim everthing and check backlash and I was good to go. It sucks when a simple job ends up like that. I know how you feel man.
 
This could be a major pain, I have thought I was going to break this several times.

A right angle drill and left hand drill bit would be my first try. Shorten the bit as much as you can if needed. A Dremel with a flex shaft might help.

With the head broke off, only the threads are holding it in, so if you can get in there with a small punch, you may be able to tap it in the out direction.
 
If that thing was so jammed in there that the bolt head broke off (assuming the bolt is siezed as opposed to metal fatigue) then no amount of pounding with a chizel and hammer is going to dislodge that bolt. I'd have to lean more towards the replacement carrier solution. I really can't even imagine being able to drill that thing out well enough to where you'd be able to preserve the threads and I doubt a Helicoil would be an ideal solution for that location.
 
Alright problem solved.
about 95% of the treads came out with the head. Just enough that i couldnt pull it out with a drill.

Solution:
dremil tool with a pointed cuting bit.
I put to holes in the bolt at oposite sides of it. I then took a punch and was able to "walk" it out by taping 1/2 turn at a time.
I got fairly lucky the way it broke.
Now i need a new bolt, i can take it off my stock carrier, i just hope the same thing dosnt happen.
Maybe i will use my best friend in the garage this time around: the propane torch.