DataImportHandler configuration - externalizing environment-specific settings?

[Erik Hatcher]

In an environment where there are developer machines, test, staging,  
and production servers there is a need to externalize DIH  
configuration options like JDBC connections strings (at least the  
database server name), username, password, and base paths for XML and  
plain text files.

How are folks handling this currently?  Didn't seem to be a way to use  
system properties like we can in solrconfig/schema.xml files using $ 
{sys.property[:defaultValue]} syntax.  Having system properties be  
available in the variable resolver would be quite useful.  Is this  
already there and I missed it?

Thanks,
        Erik