Just look for a different term that is already gender inclusive. Maybe one day us Spanish speakers will agree on gender-inclusive inflections, but currently -e is not really having any traction outside dedicated LGBT circles, and -x or -ex even less. I admit I hesitate to speak to the odd person expecting -e and I'm supposed to benefit from it catching on!
Grammatical gender just sits in a similar position to closed class words: you can't just add new gendered inflections to a language and expect speakers to still be able to speak it without effort, specially when it propagates to adjectives through linguistic agreement. Imagine if someone asked you to use tay instead of singular the or something similar.
I can't comment on pendejo/a as it isn't part of my dialect, so I'm not sure what would be equivalent with similar nuance, but I doubt anyone cares about being inclusive when insulting.
Honestly, most people (including me) don't care about gender neutrality in the latino community. In any case, pendeje is the correct way to write it and pronounce it.
should I prefer the use of the term "pendejex" to be gender inclusive in Spanish?