Since the version 1.6 you can specify a defaultDirectoryStyleName property on the searchObjectUI configuration elements; these values are used in precedence to any defaultDirectoryStyleName value defined on the associated BaseQuery.
<BaseQuery Name="WirePages" ...>
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<SearchList>
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<searchObjectUI name="Images" defaultDirectoryStyleName="Thumbs">
These defaultDirectoryStyleName will set the directory style in a new listing or if the current search (searchObjectUI) has changed.
Examples can be found in the standard configuration's WirePages and WireShell BaseQuery in shell4_config.xml that are visible in the Articles and Shell main tab's wire searches.