In that case you may want to contact Mike Stacy at Evangelyze Communications (if he doens't already reply here) as his company has a product called SmartSearch for OCS which is a web-interface for searching archived IM content. It's designed for OCS but he would know if it has been tested with LCS and whether it works or not with LCS.
http://evangelyze.net/products.asp#EC_SmartSearch
Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS