Depending on the kind of pen, assuming you CA finished, you may be able to unscrew some of the parts. Threaded parts on the blank can then be placed between centers (maybe with something to buffer the threads from the metal of the centers, like paper towel or the like). Tape of the fittings if necessary to prevent scratching, then you could lightly sand with fine grit sandpaper and then polish to clean up the blank.
If you finished with something other than CA, I'm not sure I have any recommendations...other than, at least, not to glue your parts with CA. CA can react with some platings, so it is better to use something like loctite to hold parts in place. Easier to disassembly if necessary, and won't react with platings.