Hi
After reviewing your brief I think there are a number of creative approaches to your problem however you haven't specified the nature of your podcast of the target market so this proposal will be broad at this stage, I have two key points to discuss initially.
As users don't often switch medium as you say, are you attaching your brand to other audio outlets in order to attract people? local radio, reciprocal podcasts, LinkedIn video and even publishing an audiobook (budget dependent). This would be my first recommended route especially recipricol podcasts and quickfire Q&As.
Sponsorship through affiliates could also be really beneficial, they aren't always costly and with the right campaign hook, you could see increased listeners.
I'd love to discuss this further with you before you appoint someone so please feel free to message me.
Best regards
Gemma