Is it possible to have one column fill all the available space in a column tree panel?

Here is the code I have at the moment I would like the title to fill the rest of the panel rather than be fixed width.

Code:
var tree_guidance = new Ext.ux.tree.ColumnTree({
    id: 'treeGuidance',
    layout: 'fit',
    title: 'Guidance list',
    region: 'north',
    height: 150,
    split: true,
    enableDD: true,
    rootVisible:false,
    autoScroll:true,
    listeners: {
        'click': function(n) {
            fnLoadVersions(n.attributes.id,n.attributes.typeid);
        }
    },
    columns:[
        {
            header:'ID',
            width: 150,
            dataIndex:'id'
        },{
            header:'Title',
            width: 500,
            dataIndex:'title'
        }
    ],
    viewConfig: {
        forceFit: true
    },    
    loader: new Ext.tree.TreeLoader({
        dataUrl:'/gm/ds/json_guidance_list.cfm',
        uiProviders:{
            'col': Ext.ux.tree.ColumnNodeUI
        }
    }),
    root: new Ext.tree.AsyncTreeNode({
        text:'Root'
    })
});
Any help/pointer appreciated!