Does anyone have any experience in using an Excel VBA program as a
subroutine to a non-Excel executable?

We have a fortran executable that can call some other executable as a
subroutine, and we have an Excel workbook that is initiated externally
(usually through Scheduled Tasks), processes, and terminates
automatically. Since the fortran executable doesn't write the passed
data to a separate file when it makes the subroutine call, I'm not sure
how to pass the data back and forth.

Any ideas?