There is no way to do it with the block on. Unless you want to ruin your gun.
You can pick up a pack of small punches at many hardware stores they come in varying sizes and range for $10-15.
A nail.. might work. You should grind the head flat so it doesn't slip around while your trying to punch out the pin.
Use a wooden block under the gun right next to gas block for support so you can press down on it. The trick isn't how hard your hitting, but rather effectively transfering energy from the hammer to the pins. If your gun is bouncing around or shaking a bunch everytime you strike the pin