Pin vice is cheap. Just chuck the bit up in a pin vice or better yet. Buy hex head drill bits and store 2 of them in your screw driver kit. Thats about $20 total for the Wheeler screw driver set and a 4 pack of hex head bits.
There is NO NEED to mess with the flash hole. It erodes each shot. Its easy to prove because breech plugs wear out all the time. If you cram some crud into the hole while cleaning the channel its simple just to poke it out even with a piece of copper wire. If you really want to use something on the hole, get a .035 pin gauge so you know then the plug or vent liner is wasted. If it goes in then its time for a new one.
