gramofile needs some way of running the different filters via the command
line.

Moi!

You're aware this is a tough one, aren't you? ;-) The closest I could
get meeting your request within a reasonable timespan is applying a
patch that adds perl bindings to gramofile. This still doesn't offer a
command line interface, but make it possible to write your own tools
with only a few lines of perl. (Or so I'm told--I'm rather
perl-illiterate.) What do you think?

Regards,

Daniel.