...the valve would hold pressure - without at least releasing it slowly - if you're really pushing the exhaust valve open as you say. Even if the transfer port was somehow plugged solid, air would still leak out around the stem when the valve is held open.
In any case, if the valve is really pressurized like you think it is, it will be very hard to push the check (inlet) valve open against the force of accumulated pressure. The checkvalve is large and can only be accessed through the inlet hole. Even if you can push hard enough with a needle punch or similar tool, the concentrated force will probably damage the valve.
Another approach would be to remove the valve body and s-l-o-w-l-y unscrew the two halves. After just a turn or two, any contained pressure should begin to escape with a hiss. At least this is what happens with 392 valves.
This message has been edited by pneuguy from IP address 18.104.22.168 on Dec 12, 2011 3:14 PM