[exim] wildcard lookup with LDAP?

Hello,

how can I use wildcard-lookups with LDAP?

Currently, I have the following statement:

${lookup{$local_part@$domain}lsearch*@{/etc/forwarders.txt}}}

forwarders.txt might contain entries like

user@???:    user@???
*@domain.com:    catchall@???

So sending to user2@??? would cause the email to be sent to
catchall@???. Is it possible to put this into one LDAP query? Or
would I have to split it (like: lookup user2@??? and if it
doesn't exist lookup *@domain.com)?

Regards
Marten