[Exim] per user rbl enable?

Hi Guys,

Were using Exim-3.36 and want to try using rbl_domains with an RBL host, now
we only want to do it for a few users at first, is there any way we can say

rbl_users = paul@???
rbl_domains = relays.orbs.org=127.0.0.2/reject

I've noticed recipients_reject_except and would like to know if there is
someway we can do the opposite functionality and only reject if it matches
rbl_users thats way its not enabled for every user.

Any help would be great thanks.

Paul