Force certain outgoing email attachments to be treated as binary

I’ve tried to ask something like this before, but I’m sure that I didn’t
define the problem well. I’d like to force attachments that are
currently being handled as plain text to be treated as binary files. I
essentially have to send x509 ssl certificates as files with a .txt
extension. Since they really are text files, they’re currently being
treated as such, which means that some email clients feel free to
display the content inline rather than as an attachment, as well as
potentially changing the line endings and such. Is there any practical
way to force these to be treated as binary files, even if it means
forcing all text files that go out through RT to be treated as binary
files, or forcing all plain text files on the entire server to be
treated this way?