After seeing that picture I modified my P-68 with an external rod. Works great! All ya gotta do is slam the knob with your palm and pop, the valve is charged. Makes a much better puncture on the 12 gram too, since I have a lightened hammer to begin with.
I'll post pictures on how I modified it once I'm completed with the gun.
I also fabricated a forward mounted speed loader (swaps out 10 round tubes for reloads).