You don’t. 😉
You’re barking up the wrong tree.
That person wants and needs an employee. And that’s not what you are. You’re not a substitute employee.
Which is the second part of the problem. You are still thinking of yourself as—and trying to sell yourself in the context of being—an assistant.
Remember, when you are in business, for both legal and practical reasons, you are not anyone’s assistant.
I want to challenge you to think about what you do, what you are and what administrative support is, apart from and outside of the context of assistant.
When you do that, you realize that you are an independent professional (not an assistant) with a particular specialization and expertise to offer (administrative support) in the same way that an attorney is an expert in the law and an accountant is an expert in financial matters.
Once you raise your consciousness about that, you will begin to see and define your role differently, which will lead you to market differently, which will draw and attract an entirely different audience, one that’s not looking for temps or substitute employees, but an alternative to those things.