I have used the donut caching library (mentioned by spender in the comments above) to solve a very similar problem.
Once your project has a reference to the MvcDonutCaching library, you can call an extended Html.Action
method to exclude it from the cache e.g.
// Action(this HtmlHelper htmlHelper, string actionName, string controllerName, bool excludeFromParentCache)
@Html.Action("LoginStatus", "Home", true)
To do this, you obviously would need to isolate the part you don't want to cache to its own action and partial view.