Tim,
Sure, In the GroupFilter widget Widget.html find this line:
<td class="tdData"><input type="checkbox" data-dojo-type="dijit/form/CheckBox" data-dojo-attach-point="chkPersistDef" data-dojo-props="value:true,checked:false"/> ${nls.labels.PersistDefHeading}</td>
And change checked:false to true.