http://docs.splunk.com/Documentation/Splunk/6.4.2/Knowledge/Managesummaryindexgapsandoverlaps
Use the backfill script to add other data or fill summary index gaps
The fill_summary_index.py script backfills gaps in summary index collection by
running the saved searches that populate the summary index as they would have
been executed at their regularly scheduled times for a given time range.
check this one as well.. FYI - This document refers to 3.x versions of Splunk.
http://wiki.splunk.com/Community:Summary_Indexing_Back_Fill
Did you get around with this?