This question is more about project management and change management than UX. But it's a well known situation in UX-non-mature organisations. I've met it twice personally.
It is a long path for you to build up awareness for users and to establish design processes that merge business as well as users needs. Look out for UX maturity docs - how to reach it strategically and what to do tactically.
In your situation I would give the message in the language and thought context your sponsor understands. Because you can't expect them to get your point of view yet.
If it is a business background collect KPI's and calculate business cases for usability. Check here for same cases humanfactors.com/coolstuff/roi.asp
If it is a IT background you better argue in terms of effiency, less errors, supposed user acceptance of your and other solutions (and the security issues emerging if other solutions were used stealthily) and may be what competitors do. And you can calculate costs of aditional training time because of unstardarized user journeys / software behaviours.