I think meeting your need within a ViewPanel is going to be difficult, if not impossible.
What you CAN do is add a combobox above the ViewPanel that is populated with a DbColumn pointing to the categorized column of your view. Then, when this is clicked your view will filter on the value.
Add your combobox as stated above
Add an onChange event to the combobox that sets a viewScope var (for ex. viewScope.category) with the combobox value. Set a partial refresh with the ViewPanel as the target.
<xp:comboBox id="comboBox1">
<xp:selectItems>
<xp:this.value><![CDATA[#{javascript:@Unique(@DbColumn(@DbName(),"Admin",1))}]]></xp:this.value>
</xp:selectItems>
<xp:eventHandler event="onchange" submit="true"
refreshMode="partial" refreshId="viewPanel1">
<xp:this.action><![CDATA[#{javascript:viewScope.category = getComponent("comboBox1").getValue();}]]></xp:this.action>
</xp:eventHandler>
Finally, in the ViewPanel properties, set it to filter by category name and compute the value to be your viewScope.category value.
Now, when you click the combox and select a value your view will filter on that value.