In Esperanto, each letter has only one way to be pronounced. That's one of the basic rules of Esperanto and that's what makes it so easy to pronounce and spell: there is only one way.
Therefore, a word not being in the dictionary still has to be pronounced according to the basic rules of Esperanto. You cannot pronounce the letter 'j' however you want.
Tute male: Esperanto estas dia revelacio... legu jen: http://www.esperanto.ch/svisa-espero/svisa-espero-n-ro-4-2016.html