After searching half the internet (or more) hoping in vain there is a method to use Epwing dictionaries (e.g. the excellent Wadoku German/Japanese dictionary) on a Casio Ex-Word, I decided to ask you guys. Maybe someone around here knows more than the internet. If there is any method to use Epwing dictionaries - or other free ones?

This is unfortunately something that might be difficult to do. The big dictionary companies do not want you using free dictionaries. They want to sell you the dictionaries. So a lot of them lock down their dictionaries to prevent use of all but the proprietary dictionaries they sell.