Zookeeper client for eclipse is the tool you're looking for. You can edit directly the clusterstate. http://www.massedynamic.org/mediawiki/index.php?title=Eclipse_Plug-in_for_ZooKeeper
Another option can be using the delivered zkclient (distributed with solr 4.5 and above) and upload a new clusterstate with a new shard range. Good luck
