you can create a lookup just by collecting your needed data and place it in a csv file. then upload the file to splunk. heres a link that explains how: http://docs.splunk.com/Documentation/Splunk/6.5.2/Knowledge/Usefieldlookupstoaddinformationtoyourevents
if you have the data within splunk from a different data source, you can create a search that collects the right data and arranges in a table, then use the outputlookup command to save it.
since you mentioned its a sensitive data, will recommend to restrict permissions on that lookup
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