Extjs4: TreeStore with method POST

I have a Ext.tree.Panel and define in it I have a store. I want to be able to update the store via ajax along with POST params.

Here is my tree definition:

var mytree = Ext.create('Ext.tree.Panel',{
    rootVisible:false,
    store:Ext.create('Ext.data.TreeStore', {        
        root:{
            id:'rootnode',
            nodeType:'async'         
        },
        proxy:{
            method:'post',
            type:'ajax',            
            url:'myurl'
        }
    })    
});

And I try and reload the store as follows:

mytree.store.load开发者_JAVA技巧({params:{search_string='value'}})

But the store attempts to reload with the params as GET Parameters.

Some help would be greatly appreciated. The ExtJS 4 Docs arent great at the moment (in my opinion)

---

There is actionMethods parameter in proxy to specify method of requests: http://dev.sencha.com/deploy/ext-4.0.0/docs/api/Ext.data.proxy.Ajax.html

proxy:{
    actionMethods: {
        create: 'POST',
        destroy: 'DELETE',
        read: 'POST',
        update: 'POST'
    },
    type:'ajax',            
    url:'myurl'
}