Drill a 1/8" hole on the top of the block, right above and all the way to the sear block pin. If you drill on the center, you'll en up behind the pin. Tap the hole. (For these operations you will require carbide bit and tap, as the block is made of super hard tool steel and is unmachinable with regular bits.)
Then fill up the hole with oil, and tighten a screw into the hole. The hydraulic pressure will drive the pin out. Remove the block, cut the pin to the thickness of the receiver walls, and glue in place with epoxy.
This method works about 50% of the time, as pin lenghts and positions vary. If your drilling puts you anywhere other than at the end of the pin, this method won't work. If you determine you're SOL, then its time to break out the Dremmel cutting wheel and go at it carefully.
Good luck!