I have to say from the off i know the drawing is absolutely abysmal even for a 2 year old but i have not done this in years----------------
I could not wait for answers to my needs so came up with this little idea. A vice with a piece of steel about 10in long with a 6.5mm hole at one end held in a vice vertically. Pull/break the steel part of the mechanism off the pen lower half and tap a 5mm thread into the brass, the hole in the brass is the perfect size for tapping, put a 5mm bolt through the hole and screw into the hole you tapped in the brass section of the remaining mechanism.
Now hold the lower half of the the pen and with a light hammer tap the steel bar the opposite direction you are pulling on the pen.
I use a 1/4lb hammer and it took one light tap to pull the mechanism out.
It came out really easily.
And i still feel bad about the drawing, a drunk Cat with a 6in paintbrush could do better i'm sure.