[exim] transport filter

Hi all - I'm new to Exim 4 and am having trouble. I want to run all mail
through an external filter to strip certain attachments (I already have the
program to do this - renattach). I cannot figure out how to convice exim to
push all mail through this! I have looked at other examples to do a
transport_filter, but they all seem to refer to a monolithic exim.conf, where I
have a conf.d folder and then several sub-folders (acl, main, transport,
router, etc) so I'm not sure where to put the configuration and get it to
actually work.

I'd be happy to RTFM, but can't seem to find a section that talks about this.

FWIW, I am on Ubuntu hardy and using exim 4.69.

I've already pulled out most of my hair over this, so any help would be most
appreciated!

thanks,
David