The update function does not work with attribute bindings

[rhessinger]

Is there any way to bind an update function to an attribute binding? This would be for setting classes. Currently I'm using a jquery plugin called jquery.selectBoxit and when setting a class to the select, I need to bind it to a sibling. Having the ability to set the class through a custom update function will fix the problem. The update function would follow the standard bindings function.

Here is the syntax it tried:

bindings:{
    '#tb-input': {
        observe: 'Input',
        attributes: [
            {
                name: "class", 
                observe: "IsNotDescriptionConfident", 
                onGet: "GetClassStringFnc",
                update: "UpdateClassFnc"
             }]
        }, 
    }
}