KrisRowAs far as I know, no converter can fit into this version of Ohto.
Instead of keep buying the cartridge, one can clean the used cartridge, and then refill the empty (used) cartridge with ink of one's choice using a syringe.
KrisRowIt looks like the answer to your question is "no". In the description you'll find the following:
"Like all OHTO fountain pens, the Poche accepts international standard short cartridges, but cannot take a converter due to its compact size."