You could set the default bucket properties, but I would advise against that since you might some day want an un-indexed bucket.
Edit Following up on this - Riak 1.4 will let you set the boolean search
property, but Riak prior to 1.4 requires that the commit hooks be specified when enabling search on a bucket. If you truly need to index everything that you're saving into Riak, my only current suggestion would be to dump the data into SOLR/Lucene automatically rather than attempt to put some complex semantics around enabling Riak Search the first time an object is written into a bucket.