Specifying backup location in solrconfig.xml

[Dietrich]

I am using Solr Replication to create a snapshot for backup purposes
after each optimize:
<requestHandler name="/replication" class="solr.ReplicationHandler" >
    <lst name="master">
        <str name="backupAfter">optimize</str>
    <str 
name="confFiles">schema.xml,mapping-ISOLatin1Accent.txt,protwords.txt,stopwords.txt,synonyms.txt,elevate.xml</str>
    </lst>
</requestHandler>


That works fine, but i need to create the snapshots somewhere outside
the data directory. I tried specifying a location like this:
<str name="location">${solr.home}/backup/site</str>
or
<str name="location">/opt/solr/backup/site</str>

but Solr is complaining:
SEVERE: java.io.IOException: Cannot run program "snapshooter" (in
directory "solr/bin"): java.io.IOException: error=2, No such file or
directory

How can I specify the location for the backup in solrconfig.xml

Dietrich