Mais feio que encoxar a mãe no tanque...

gistfile1.js

FormFieldMask = {
    money: {
        event: 'keyup',
        regex: /[^\d,]/g,
        handler: function(event){
            var field = event.target;
            field.setValue(field.value.replace(FormFieldMask.money.regex, ''));
        }
    },

    integer: {
        event: 'keyup',
        regex: /[^\d]/g,
        handler: function(event){
            var field = event.target;
            field.setValue(field.value.replace(FormFieldMask.integer.regex, ''));
        }
    },

    // Magically applies the masks defined above
    apply: function(){
        for (attr in FormFieldMask){
            if (FormFieldMask.hasOwnProperty(attr) && attr != 'apply'){
                eval("$j('."+attr+" input')."+FormFieldMask[attr].event+"(FormFieldMask."+attr+".handler);");
            }
        }
    }
};