fill_between() path and country border paths

I am plotting an open fill path over a U.S. map for which I'd like to extend the filling all the way to the closest border of U.S.

I thought I could use fill_between() my path and the path in the borders path list returned by drawcountries() that is closest to mine. So, I've been looking for examples on how to use fill_between() when 2 paths are known with no much luck for several days.

Does anyone know a better approach to solve this issue?

Does anyone know where I could find an example for fill_between() with 2 given paths as opposed to between 2 curves plotted in the same plot?