[Exim] setting drop_cr for the cyrus user only

Hi all,

how can I set the drop_cr option (in Exim 4) to true only for the cyrus
user?

drop_cr = ${if eq{$caller_uid}{60}{true}{false}}

does not work:

Exim configuration error:
"" is not a valid value for the "drop_cr" option

Thanks
     Oliver