manual created select control and form_state

Hi,
I have a piece of code that creates a select type control this way:

        $selectEntitie = "<label for='selectEntitie'>";
        $selectEntitie .= "&nbsp;".t('Entities').":"."&nbsp;";
        $selectEntitie .= "<select id='FK_entities' name='FK_entities' onChange='document.getElementById(\"idRefreshGlpiPermissions\").click();'>";
        $selectEntitie .= "<option value='null' >--".t('Select an entity')."--</option>";
    	if ( isset($estructura['entities']) && count($estructura['entities']) ){
    	    foreach ($estructura['entities'] as $indice => $valor){
    	        $selectEntitie .= "<option value='".$indice."'>".$valor."</option>";
    	    }
    	}
        $selectEntitie .= "</select></label>";

Then, this text is added to the form array as prefix section of a markup type element.
Is there any way to get the selected value of the control in the $form_state['values'] var?