[Exim] rbl_domains and 4xx errors

Using exim 3.34, is there a way to have exim reject recipients with a
4xx error instead of a 5xx error using rbl_domains? I'm using
bl.spamcop.net right now (as 'warn' instead of 'reject' since spamcop's
bl is pretty aggressive). But, instead of warnings in the logs, I'd like
to temporary reject with a 4xx error.

Paul