invert the die and tap the decapping pin back through the flash hole- you'll need a hammer and something like a finishing nail with the point ground off- point to point, tap gently, and maybe put it your padded vise- see how that works- or the shaft off a drill bit- 5/64's or 1/16th shaft- the flashole typically is 3/32, so a 5/64 is the best you can do- inverted, the rod shoud drop to the neck once it's no longer held by the head
you could also put the die in your press and simply pull up and twist at the same time,provided you figure out how to hang on to the decapping rod- i mention that in passing b/c if you do it that way, you're going to use something like vice grips or pliers, and those can damage the shaft, esp rcbs, which uses a threaded rod