Sort vs data type

Is there a way to sort a treecol according to the data type of the treecell ?

Here is a tree example : I would like to sort a tree column in a numerical 
order,

<tree id="trCntrcEndrsHstry"
       flex="1"
       datasources="rdf:null"
       ref="urn:test"
       enableColumDrag="true"
       flags="dont-build-content">
   <treecols>
     <treecol id="trcl1"
              label="Number"
              sortActive="false"
              sortDirection="ascending"
              sort="?sort_number"/>
   </treecols>
   <template>
     <rule>
        <conditions>
         <content uri="?nbr_lst"/>
         <member container="?nbr_lst" child="?nbr"/>
         <triple subject="?nbr"
                 predicate="http://test#nbr"
                 object="?sort_number"/>
       </conditions>
       <action>
         <treechildren flex="1">
           <treeitem uri="?nbr">
             <treerow>
               <treecell label="?sort_number"/>
             </treerow>
           </treeitem>
         </treechildren>
       </action>
     </rule>
   </template>
</tree>

How shoud I proceed in JS ? Is there a way to replace the compare function 
of the nsIXULTreeBuilder ?