If I remember correctly, in simple xml you can have then in your table, but in the fields option for the table you can specify the fields. The data is still present, but not shown to the user.
For example, here I show the time, systemFrom and systemTo to the user, but on drilldown I grab the eventId value from that row and use this later on.
<table>
<search>
<query><![CDATA[
index=myIndex host=myHost
...
]]></query>
</search>
<fields>_time, systemFrom, systemTo </fields>
<option name="drilldown">row</option>
<drilldown>
<condition field="*">
<set token="myEventId">$row.eventId$</set>
</condition>
</drilldown>
</table>
... View more