You could render the component in all phases except the renderphase. This would allow to set the value during update phase, but would hide it to the client.
Here is an example: Conditionally hidden edit box in a partially refreshed panel
EDIT:
<xp:this.rendered>
<![CDATA[#{javascript:
if( view.isRenderingPhase() ){
return InvolvedManager.hasPartyType();
}else{
return true;
}
}]]>
</xp:this.rendered>