How to cast a "seeded" pen blank without a custom made mold.

[Aussie Chris]

Hi.. I am looking for information on how to cast a "seeded" resin blank.
I want to glue some seeds to the tube, and then make it into a resin blank,
but I am unsure as how to make it so that the resin does not get into the tube.

I am in Australia, and am new to pen making.

any suggestions are most welcome and appreciated
Cheers
Chris