Since the Copic markers are alcohol based and you can also use 90% alcohol to blend pencils (tutorial on the Prismacolor site), it makes sense to just use their blender rather than fill an empty pen...not sure what their blending solution is, but - it does work.
Dina Kowal Creative ♥ Original Art Prints
If you hear a voice within you say you cannot paint,
then by all means paint, and that voice will be silenced.
Vincent Van Gogh