[Exim] Pipe return_output vs return_fail_output

Hi all,

I have a pipe transport that currently uses return_fail_output. It works
as expected except that the error message sent back shows the command
path and the exit code.

If I use return_output then I get a much nicer looking error message that
doesn't display the command path or exit code.

Problem is I can't use return_output because it doesn't honour EX_TEMPFAIL.

Is there any way to make the error message for return_fail_output look
like the one for return_output? It doesn't look like errmsg_file will
eliminate the command path and exit code while retaining the failed
address, but perhaps I'm missing something.

Mark