Using custom user variables in the API Explorer

Hi there!

I am trying to pre-fill a custom header required for our API.
I have set it in the JWT, and can see it in markdown rendered content using MYVARIABLE.
However I don't know how to set the value in my OAS specification. I've tried setting the example to MYVARIABLE, but that doesn't seem to do anything.

Is what I'm trying to do possible?