[Exim] recursive regmatch

I'm trying to strip off all third level domain
information from my local domains

host.domain.de -> domain.de

/etc/exim/localdomains:
domain.de

But since I have all my local domains in a file
I don't want to have to add a rewriting rule
by hand. Of course that would be just

*@*.domain.de $1@???

But I tried it this way:

*@* "$1@\
       ${lookup{\
            ${if match{$2} {^[^\\\\.]+(.*)\\$}\
                {\
                   ${if match{$2} {^[\\\\.]+(.*)\\$}\
                      { here should be the result of the 2nd match,
                        but $1 doesn't work }
                      { here should be the $2 before the match }
                    }\
                }\
                {$2}\
             }\
       } lsearch{/etc/exim/localdomains} {$value} {$2} }"

How do make it work?
Maybe there a better solution?
--
Torsten